Maternal Intake of Magnesium, Calcium, and Calcium Supplements: Association with Preterm Birth Risk in a Nested Case-Control Study

Maternal Intake of Magnesium, Calcium, and Calcium Supplements: Association with Preterm Birth Risk in a Nested Case-Control Study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Maternal Intake of Magnesium, Calcium, and Calcium Supplements: Association with Preterm Birth Risk in a Nested Case-Control Study Zifu Wang, Lei Cao, Yuqing Li, Chenyan Yang, Baohong Mao, Liping Yang, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7305270/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Objective To explore the association between magnesium (dietary), calcium (dietary), and calcium supplements intake levels before and during pregnancy and the risk of Preterm birth (PTB). Methods The study subjects were pregnant women who registered at the Perinatal Medicine Center of Gansu Provincial Maternal and Child Health Hospital between March 2018 and March 2019 and whose birth outcomes could be followed up. After obtaining informed consent and ethical approval, a one-on-one dietary nutrition survey was conducted during pregnancy. A database was established based on overall dietary intake levels for statistical analysis. PTB was used as the outcome variable, and intake levels of different substances during pregnancy were used as independent variables. Unconditional logistic regression model was used to calculate the odds ratio (OR) and its 95% confidence interval (95% CI), in order to analyze the impact of different levels of substance intake on PTB. Multivariate-adjusted restricted cubic spline (RCS) models explored the nonlinear association between dietary magnesium/calcium intake and PTB risk. Results A total of 8897 pregnant women were included in the study, with 880 in the case group and 8017 in the control group. Multivariate logistic regression analysis revealed that low magnesium intake in third trimester and inadequate calcium supplements intake elevate the risk of PTB. Similarly, low calcium intake before and during pregnancy also increases this risk. Moreover, magnesium, calcium, and calcium supplements exert a synergistic effect on the risk of PTB. Conclusion During the third trimester, intake of magnesium and calcium supplements should be increased. Additionally, to prevent PTB, calcium intake should be enhanced preconception and during pregnancy. Magnesium Calcium Calcium supplements Intake levels PTB Nested case-control study Figures Figure 1 Figure 2 Introduction According to WHO criteria, PTB refers to delivery prior to 37 weeks of pregnancy [ 1 ] . PTB is the second largest direct cause of child deaths in children younger than 5 years, and PTB affects both high-income and low-to-middle-income countries, with incidence rates ranging from 5–18%, of which approximately 60% occur in low-and middle-income countries [ 2 ] . Epidemiological data compiled from a Chinese systematic review established the national PTB rate to be 5% [ 3 ] . PTB constitutes a major determinant of adverse neonatal outcomes and mortality [ 4 ] . PTB is associated with increased risks of respiratory distress syndrome, cerebral palsy, and other developmental disorders. Moreover, preterm infants may face elevated susceptibility to certain chronic non-communicable diseases in later life [ 5 ] . Studies have demonstrated that maintaining optimal nutrition throughout gestation plays a pivotal role in mitigating adverse obstetric outcomes and ensuring long-term maternal and fetal well-being [ 6 ] . Adequate maternal nutritional intake and improved health status preconception and during gestation positively influence fetal growth and development, optimize pregnancy outcomes, and increase perinatal survival rates [ 7 ] . Deficiencies in trace elements are prevalent during both preconception and pregnancy periods, necessitating increased dietary intake of essential micronutrients [ 8 ] . Evidence suggests that magnesium modulates uterine smooth muscle activity, indicating that maternal magnesium intake may influence gestational duration. However, current literature remains limited regarding the association between magnesium supplementation and PTB risk [ 9 ] Magnesium therapy demonstrates neuroprotective effects during the perinatal period and shows particular efficacy in preventing neurological damage in preterm infants [ 10 ] . Magnesium is an essential micronutrient involved in numerous physiological processes, including muscular relaxation, skeletal development, electrolyte homeostasis, and blood pressure regulation. Given these critical functions, maintaining adequate magnesium status during pregnancy is of paramount importance. However, achieving optimal magnesium supplementation in the prenatal period presents significant clinical challenges, despite the availability of multiple intake modalities [ 11 ] . Calcium deficiency augments myometrial contractility by modulating muscular cell tension, consequently triggering preterm labor [ 12 ] . Evidence indicates widespread calcium insufficiency among pregnant women in low- and middle-income countries. Systematic reviews demonstrate that calcium supplements during pregnancy significantly reduces pregnancy-related complications, including pre-eclampsia, maternal morbidity and PTB. While WHO recommends a daily calcium intake of 1.5g-2g for pregnant women, emerging evidence suggests that 1g/day may achieve comparable clinical benefits in certain populations [ 13 ] . Population-based studies reveal a high prevalence of inadequate dietary calcium intake (85.9%). Maternal calcium supplements during gestation demonstrates a significant inverse association with PTB risk [ 14 ] . Current evidence remains limited regarding the associations between magnesium/calcium status and PTB risk. Even fewer studies have examined the combined effects of magnesium and calcium supplements, with virtually no research investigating the potential synergistic interactions among these micronutrients in relation to PTB. Materials and Methods Study population A birth cohort study was conducted from January 2018 to June 2019 at the largest hospital of its kind in Lanzhou City, Gansu Province. Eligible participants were pregnant women aged 18 years or older, without a history of mental illness, who received regular prenatal care and provided written informed consent. The study included a total of 8897 eligible women, comprising 880 who delivered preterm infants and 8017 who delivered at term. The study protocol was approved by the Institutional Review Board of the Maternal and Child Health Hospital of Gansu Province [2018 (029)], and all participants provided written informed consent [ 15 ] . Dietary surveys, magnesium, calcium and calcium supplements daily intake Daily surveys and dietary magnesium, calcium and calcium supplements were collected through a face-to-face semi-quantitative food frequency questionnaire (FFQ) [ 16 ] . The survey covered sociological characteristics, disease history, physiological fertility, and dietary intake. Dietary status was assessed using a 24-hour dietary recall survey conducted by trained medical staff. Participants reported the types and quantities of all foods consumed over three consecutive days, covering 12 main categories: cereals, oils and fats, vegetables, fruits, poultry, livestock meat and its products, eggs, aquatic products, beans and soy products, milk and milk products, bacteria and algae, snacks and drinks, as well as 59 other common food items. After obtaining the informed consent from the patients, four dietary and nutritional surveys were conducted on all the research subjects. The first survey was carried out during the 3-month period preconception when they came to the hospital for preconception consultation and health check-ups. The other three surveys were conducted during the early pregnancy (≤ 13 weeks of gestation), the middle pregnancy (14–27 weeks of gestation), and the late pregnancy (≥ 28 weeks of gestation) when they came to the hospital for prenatal check-ups. After completing all dietary surveys, the daily intake of dietary vitamins and trace elements of each pregnant woman during different pregnancies was calculated following the second edition of the Chinese Food Composition Table 2009 [ 17 ] Daily vitamin and trace element intakes in different pregnancies were divided into groups based on the recommended nutrient intake (RNI) of Chinese residents [ 18 ] for statistical analysis. The RNI is the amount of a nutrient that is enough to ensure that the needs of 97. 5% of the population are met. Data on pregnancy-related complications and birth outcomes were extracted from medical records. Preterm Labor Preterm labor (PTB) is defined as a live birth occurring before the completion of 37 weeks of gestation, and such cases were included in the case group for analysis. Non-PTB, defined as delivery at or beyond 37 weeks of gestation (full-term delivery), was included in the control group for analysis. Deliveries were further stratified into three categories: <32 weeks, ≦32 < 34 weeks, and ≦ 34 < 37 weeks. Body mass index (BMI) and gestational weight gain Preconception weight was self-reported during the first prenatal care visit. BMI was calculated as weight (kg) divided by the square of height (m), and then subcategorized in accordance with the Working Group of Obesity in China as follows: underweight (BMI < 18. 5 kg/m2), normal weight (18. 5 kg/m2 ≤ BMI < 24 kg/m2), overweight (24 kg/m2 ≤ BMI < 28 kg/m2), and obesity (BMI ≥ 28 kg/m2). Gestational weight gain in kg was calculated by subtracting pre-pregnancy weight from maternal weight at delivery, which was categorized based on the US Institute of Medicine (IOM) GWG Guidelines 2009 [ 19 ] . Covariates The study covariates included maternal age, body mass index (BMI) during pregnancy, maternal education level, household income per capita, alcohol consumption during pregnancy, smoking status during pregnancy (active and passive smoking), maternal employment status (employed during pregnancy, never employed, or not employed only during pregnancy), presence of gestational hypertension, history of PTB, presence of gestational diabetes mellitus, parity (primipara or multipara), and neonatal sex. Statistical analysis Comparisons of the selected characteristics between women with PTB and Non-PTB were evaluated using the chi-square test or Fisher's exact test. The differences in measurement data between the two groups were analyzed by independent-sample t test, and the variables that did not meet the normal distribution were compared between groups by the Wilcoxon rank-sum test. Unconditional logistic regression was used to determine the odds ratios (ORs) and 95% confidence intervals (CIs) for the association between dietary magnesium, calcium and calcium supplements intake and the risk of PTB and its clinical subtypes. Confounding factors, including weight gain during pregnancy, maternal BMI, total energy intake, monthly income per capita, maternal education level, smoking, maternal employment, multivitamin supplementation, gestational hypertension, history of PTB, and reproductive history, were adjusted for in the unconditional logistic regression models. Dietary magnesium and calcium intake were categorized into quartiles, and the dose–response relationship (P for trend) was calculated based on those categorical levels. The association between dietary magnesium, calcium and calcium supplements intake and the risk of PTB may result in a nonlinear correlation. Multivariate-adjusted restricted cubic spline (RCS) models with three knots were applied to explore the nonlinear association. The number of knots was determined by comparing the criteria between Bayesian and Akaike information. The RCS models were adjusted for the potential confounding factors listed above. The multiplicative interaction parameters [OR = OR11/(OR01 × OR10)] and 95% CI were also estimated by including the abovementioned variables [ 20 ] . Cut-off values for magnesium and calcium were determined for four gestational periods (preconception, first trimester, second trimester, and third trimester) using SPSS version 26 for windows, We estimated 95% CI for each of these measures; the null values of RERI and AP were 0, whereas the null value for S was 1. All statistical tests were two-sided. Analyses were performed using SAS 9. 4 (SAS Institute, Inc, Cary, NC, USA). The RCS models were performed by R software, version 4. 4. 2(package 'Hmisc', 'rms', and 'survival'). Results Basic characteristics of the study population A total of 8897 eligible women participated, including 880 who delivered preterm infants and 8017 who delivered at term. As illustrated in distributions of selected characteristics of the study population (Table 1 ), mothers of preterm infants, compared to those of Non-PTB infants, exhibited lower household monthly income, lower educational attainment, reduced employment rates, higher prevalence of gestational hypertension, increased smoking rates, and a greater likelihood of gestational diabetes, history of PTB, and multiparity. Additionally, mothers in the case group exhibited significantly lower maternal weight gain and reduced total energy intake compared to the control group. However, no significant differences were observed between the two groups regarding alcohol consumption during pregnancy or neonatal sex. Table 1 Distributions of selected characteristics of the study population Characteristics preterm(n = 880) term(n = 8017) χ² P-value Maternal age 75.813 < 0.001 <23 110(1.24) 504(5.66) 23≤ ~ <26 135(1.52) 1192(13.40) 26≤ ~ <30 270(3.03) 3453(38.81) ≥30 365(4.10) 2868(32.24) pregnancy BMI 7.693 0.021 <18.5 176(1.98) 1709(19.21) 18.5≤ ~ <24 583(6.55) 5450(61.26) BMI ≥ 24 121(1.36) 858(9.64) Maternal education level 179.736 < 0.001 ≤middle school 333(3.74) 1577(17.73) middle school< ~ ≤Community college 340(3.82) 3215(36.14) ≥college 207(2.33) 3225(36.25) household income per capita 88.84 < 0.001 ≤2000 340(3.82) 1945(21.86) 20005000 64(0.72) 901(10.13) Drink during pregnancy 1.723 0.189 yes 3(0.03) 12(0.013) no 877(9.86) 8805(89.97) Smoking(passive smoke,active smoke) 7.853 0.005 yes 209(2.35) 6433(72.31) no 671(7.54) 1584(17.80) Maternal employment status 51.96 < 0.001 employed during pregnancy 381(4.28) 4432(49.81) never employed 357(4.01) 2384(26.80) Not employed only during pregnancy 142(1.60) 1201(13.50) Gestational hypertension 267.887 < 0.001 yes 142(1.60) 291(3.27) no 738(8.29) 7726(86.84) History of premature birth 138.781 < 0.001 yes 62(0.70) 107(1.20) no 818(9.19) 7910(88.91) Gestational diabetes 4.89 0.027 yes 15(0.17) 74(0.83) no 865(9.72) 7943(89.28) Childbearing history 60.898 < 0.001 Primipara 549(6.17) 5983(67.25) Multipara 331(3.72) 2043(22.86) Neonatal sex 0.498 0.481 Male 4103(51.18) 443(50.34) Female 3726(46.48) 382(43.41) Missing 188(2.34) 55(6.25) Associations of maternal dietary magnesium intake with the risk of PTB As shown in associations of maternal dietary magnesium intake with the risk of PTB (Table 2 ), preconception group with low magnesium intake had a significantly increased risk of PTB (OR = 1.589, 95% CI: 1.372–1.841). The risk of PTB decreased after each increase of one quartile interval. After adjusting for confounding factors, the risk of PTB still increased (OR = 1.107, 95% CI: 0.916–1.339). The first trimester was almost the same as preconception. In the subgroup of the second trimester with low magnesium intake, the risk of low magnesium intake group was significantly increased in subgroup 32 ≤ weeks < 34 (OR = 1.411, 95% CI: 0.910–2.187), and the risk decreased by 1.262 (1.019–1.562) after each increase of one quartile interval (P for trend = 0.0328). In the third trimester subgroup with low magnesium intake, the risk of PTB was almost the same as that in the second trimester. (Fig. 1) Restricted cubic spline models of PTB risk associated with magnesium intake preconception (A), at the first trimester (B), at the second trimester (C), and at the third trimester (D), illustrates the RCS curve of dietary magnesium intake preconception and during pregnancy PTB risk. As daily magnesium intake increases, the risk of PTB decreases and then stabilizes. When intake is at first trimester(359.193–583.690) mg/d, second trimester(369.733–603.250) mg/d, third trimester(365.228-908.135) mg/d, magnesium may serve as a protective factor against PTB. Table 2 Associations of maternal dietary Magnesium intake with the risk of PTB Dietary Magnesium intake(mg/d) Term (8017) Preterm (< 37weeks) cases(880) OR a (95%CI) OR b (95%CI) < 32weeks 32 ≤ weeks < 34 34 ≤ weeks < 37 n OR b (95%CI) n OR b (95%CI) n OR b (95%CI) Preconception ≥222.1193 5973 570 1.000 1.000 96 1.000 102 1.000 372 1.000 <222.1193 2044 310 1.589(1.372–1.841) 1.038(0.858–1.255) 66 1.242(0.832–1.855) 68 1.326(0.886–1.986) 176 0.909(0.718–1.151) Per interquartile increase 1.212(1.138–1.291) 1.016(0.923–1.119) 0.961(0.777–1.189) 1.044(0.848–1.285) 1.022(0.908–1.150) P for trend < 0.0001 0.7462 0.7132 0.6842 0.7223 First trimester ≥293.3383 5540 497 1.000 1.000 81 1.000 89 1.000 327 1.000 <293.3383 2477 383 1.724(1.496–1.985) 1.124(0.932–1.356) 81 1.279(0.858–1.906) 81 1.305(0.877–1.943) 221 1.046(0.830–1.319) Per interquartile increase 1.266(1.188–1.349) 1.036(0.943–1.137) 1.084(0.882–1.332) 1.090(0.892–1.332) 1.011(0.902–1.134) P for trend < 0.0001 0.4627 0.4430 0.3994 0.8492 Second trimester ≥354.0812 3957 328 1.000 1.000 54 1.000 54 1.000 220 1.000 <354.0812 4060 552 1.640(1.421–1.893) 1.146(0.938–1.399) 108 1.080(0.692–1.683) 116 1.411(0.910–2.187) 328 1.095(0.858–1.397) Per interquartile increase 1.272(1.193–1.355) 1.039(0.943–1.143) 1.008(0.815–1.246) 1.262(1.019–1.562) 0.991(0.881–1.116) P for trend < 0.0001 0.4438 0.9411 0.0328 0.8868 Third trimester ≥309.5003 5321 456 1.000 1.000 65 1.000 81 1.000 310 1.000 <309.5003 2696 424 1.835(1.595–2.111) 1.267(1.043–1.541) 97 1.830(1.182–2.832) 89 1.341(0.886–2.029) 238 1.143(0.899–1.453) Per interquartile increase 1.316(1.235–1.404) 1.102(1.000-1.215) 1.274(1.020–1.591) 1.221(0.988–1.509) 1.026(0.911–1.155) P for trend < 0.0001 0.0504 0.0329 0.0641 0.6717 OR a univariate analyses. OR b adjusted for weight gain during pregnancy,Mother's BMI, Mother's age,Gestational diabetes,total energy intake, monthly income per capita, maternal education level, smoking, maternal employ, multivitamin supplement, gestational hypertension, history of premature birth, reproductive history, dietary calcium intake and Supplement calcium. Associations of maternal dietary calcium intake with the risk of PTB As shown in associations of maternal dietary calcium intake with the risk of PTB (Table 3 ), the risk of PTB was significantly increased in the group with low calcium intake preconception (OR = 1.834, 95% CI: 1.594–2.109). The risk decreased after each increase of one quartile interval (OR = 1.306, 95% CI: 1.225–1.393, P for trend < 0.0001). After adjusting for confounding factors, the risk still increased, and it decreased after each increase of one quartile interval. Moreover, in subgroup 34 ≤ weeks < 37, the risk of PTB in the group with low calcium intake was more significant (OR = 1.390, 95% CI: 1.113–1.736), and the risk decreased after each increase of one quartile interval (OR = 1.154, 95% CI: 1.029–1.294, P for trend = 0.0145). The results of the first trimester, second trimester, and third trimester were almost the same as those preconception. (Fig. 2) Restricted cubic spline models of PTB risk associated with calcium intake preconception (A), at the first trimester (B), at the second trimester (C), and at the third trimester (D), illustrates the RCS curve of dietary calcium intake preconception and during pregnancy PTB risk. As daily calcium intake increases, the risk of PTB decreases and then stabilizes. When the intake levels are at preconception (443.608–1074.897) mg/d, first trimester (629.253-1091.939) mg/d, second trimester (674.119-1205.243) mg/d, and third trimester (678. 187–2493. 333) mg/d, calcium may serve as a protective factor against PTB. Table 3 Associations of maternal dietary Calcium intake with the risk of PTB Dietary calcium intake(mg/d) Term (8017) Preterm (< 37weeks) cases(880) OR a (95%CI) OR c (95%CI) < 32weeks 32 ≤ weeks < 34 34 ≤ weeks < 37 n OR c (95%CI) n OR c (95%CI) n OR c (95%CI) Preconception ≥359.2753 5171 438 1.000 1.000 74 1.000 84 1.000 280 1.000 <359.2753 2846 442 1.834(1.594–2.109) 1.305(1.088–1.564) 88 1.209(0.811–1.803) 86 1.046(0.706–1.551) 268 1.390(1.113–1.736) Per interquartile increase 1.306(1.225–1.393) 1.149(1.047–1.261) 1.143(0.928–1.408) 1.087(0.890–1.328) 1.154(1.029–1.294) P for trend < 0.0001 0.0035 0.2094 0.4146 0.0145 First trimester ≥529.9334 5209 427 1.000 1.000 69 1.000 79 1.000 279 1.000 <529.9334 2808 453 1.968(1.711–2.264) 1.385(1.155–1.660) 93 1.481(0.995–2.205) 91 1.354(0.920–1.992) 269 1.370(1.095–1.713) Per interquartile increase 1.337(1.253–1.425) 1.123(1.028–1.227) 1.248(1.022–1.524) 1.207(0.996–1.463) 1.069(0.959–1.191) P for trend < 0.0001 0.0101 0.0295 0.0545 0.2271 Second trimester ≥550.5764 5204 422 1.000 1.000 69 1.000 70 1.000 283 1.000 <550.5764 2813 458 2.088(1.746–2.309) 1.415(1.181–1.696) 93 1.590(1.069–2.365) 100 1.842(1.250–2.716) 265 1.276(1.021–1.595) Per interquartile increase 1.363(1.278–1.454) 1.176(1.082–1.279) 1.208(0.987–1.479) 1.160(0.953–1.412) 1.144(1.025–1.278) P for trend < 0.0001 0.0001 0.0669 0.1393 0.0169 Third trimester ≥529.4478 5498 437 1.000 1.000 59 1.000 78 1.000 300 1.000 <529.4478 2519 443 2.213(1.923–2.456) 1.503(1.249–1.809) 103 2.397(1.563–3.675) 92 2.016(1.353–3.005) 248 1.188(0.946–1.492) Per interquartile increase 1.411(1.322–1.506) 1.193(1.091–1.306) 1.457(1.178–1.802) 1.201(0.987–1.463) 1.129(1.012–1.260) P for trend < 0.0001 0.0001 0.0005 0.0679 0.0303 OR a univariate analyses. OR c adjusted for weight gain during pregnancy,Mother's BMI, Mother's age,Gestational diabetes,total energy intake, monthly income per capita, maternal education level, smoking, maternal employ, multivitamin supplement, gestational hypertension, history of premature birth, reproductive history, dietary magnesium intake Supplement calcium. Associations of maternal calcium supplements with the risk of PTB As shown in associations of maternal calcium supplements with the risk of PTB (Table 4 ), preconception, first trimester and the second trimester, the risk of PTB did not significantly increase among non-users of calcium supplements. However, in the third trimester, the risk of PTB significantly increased in non-users of calcium supplements (OR = 1.498, 95% CI: 1.284–1.747). Even after adjusting for confounding factors, the risk of PTB still increased, especially in the subgroup < 32 weeks the risk of PTB in non-users of calcium supplements was even more significant (OR = 3.065, 95% CI: 1.954–4.809). Table 4 Associations of maternal Calcium supplements with the risk of PTB Calcium supplements Term (8017) Preterm (< 37weeks) cases(880) OR a (95%CI) OR d (95%CI) < 32weeks 32 ≤ weeks < 34 34 ≤ weeks < 37 n OR d (95%CI) n OR d (95%CI) n OR d (95%CI) Preconception Users 242 27 1.000 1.000 4 1.000 4 1.000 19 1.000 Non useres 7775 853 0.983(0.657–1.473) 0.942(0.617–1.437) 158 1.122(0.405–3.105) 166 1.093(0.395–3.024) 529 0.858(0.525–1.403) First trimester Users 356 33 1.000 1.000 4 1.000 7 1.000 22 1.000 Non useres 7661 847 1.193(0.829–1.716) 1.127(0.7721.646) 158 1.650(0.598–4.558) 163 0.990(0.452–2.166) 526 1.067(0.678–1.677) Second trimester Users 2421 297 1.000 1.000 58 1.000 58 1.000 181 1.000 Non useres 5596 583 0.849(0.733–0.984) 0.861(0.738–1.005) 104 0.769(0.551–1.072) 112 0.800(0.576–1.111) 367 0.881(0.729–1.065) Third trimester Users 2958 247 1.000 1.000 23 1.000 50 1.000 174 1.000 Non useres 5059 633 1.498(1.284–1.747) 1.310(1.116–1.538) 139 3.065(1.954–4.809) 120 1.177(0.836–1.658) 374 1.114(0.919–1.350) OR a univariate analyses. OR d adjusted for weight gain during pregnancy,Mother's BMI, Mother's age,Gestational diabetes,total energy intake, monthly income per capita, maternal education level, smoking, maternal employ, multivitamin supplement, gestational hypertension, history of premature birth, reproductive history ,dietary calcium intake and dietary magnesium intake. Interaction effects of maternal dietary magnesium and calcium intake on the risk of PTB As shown in interaction effects of maternal dietary magnesium and calcium intake on the risk of PTB (Table 5 ), preconception and third trimester increase the risk of PTB in the case of high magnesium and low calcium, with the risks being (OR = 1.683, 95% CI: 1.392–2.036) and (OR = 1.855, 95% CI: 1.472–2.338) respectively. After adjusting for confounding factors, The risks of preconception were (OR = 1.307, 95% CI: 1.059–1.614) and (OR = 1.446, 95% CI: 1.116–1.873) respectively, the risk of PTB is significantly increased in the case of low magnesium and low calcium (OR = 1.255, 95% CI: 1.188–1.325), and the risk remains significant after adjusting for confounding factors (OR = 1.091, 95% CI: 1.019–1.161). The risks of PTB in during pregnancy, first trimester, second trimester and third trimester are basically the same as those preconception when the magnesium and calcium levels are low. Moreover, there is a multiplicative interaction among preconception, during pregnancy, first trimester, second trimester and third trimester, and the interaction in the third trimester is the most significant (OR = 1.691, 95% CI: 1.405–2.035, P < 0.01). Table 5 Interaction effects of maternal dietary Magnesium and Calcium intake on the risk of PTB Maternal dietary intake term preterm OR a (95%CI) OR e (95%CI) Preconception High Magnesium high calcium 4769 400 1 1 High Magnesium low calcium 1204 170 1.683(1.392–2.036) 1.307(1.059–1.614) Low Magnesium high calcium 402 38 1.062(0.892–1.263) 0.975(0.808–1.178) Low Magnesium low calcium 1642 272 1.255(1.188–1.325) 1.091(1.019–1.161) Multiplicative interaction: OR(95%CI) = 1.248(1.045–1.489) P = 0.0144 During pregnancy High Magnesium high calcium 4316 345 1 1 High Magnesium low calcium 698 87 1.559(1.216–1.999) 1.135(0.858–1.502) Low Magnesium high calcium 1050 94 1.058(0.940–1.192) 0.993(0.861–1.145) Low Magnesium low calcium 1953 354 1.314(1.247–1.385) 1.181(1.087–1.283) Multiplicative interaction: OR(95%CI) = 1.622(1.346–1.954) P < 0.01 First trimester High Magnesium high calcium 4503 366 1 1 High Magnesium low calcium 1037 131 1.554(1.259–1.919) 1.077(0.929–1.491) Low Magnesium high calcium 706 61 1.031(0.895–1.187) 0.925(0.789–1.085) Low Magnesium low calcium 1771 322 1.308(1.240–1.379) 1.151(1.067–1.243) Multiplicative interaction: OR(95%CI) = 1.501(1.252–1.801) P < 0.01 Second trimester High Magnesium high calcium 3512 274 1 1 High Magnesium low calcium 445 54 1.555(1.143–2.116) 1.141(0.811–1.605) Low Magnesium high calcium 1692 148 1.059(0.954–1.175) 1.039(0.916–1.179) Low Magnesium low calcium 2368 404 1.298(1.230–1.370) 1.163(1.065–1.271) Multiplicative interaction: OR(95%CI) = 1.525(1.269–1.832) P < 0.01 Third trimester High Magnesium high calcium 4582 351 1 1 High Magnesium low calcium 739 105 1.855(1.472–2.338) 1.446(1.116–1.873) Low Magnesium high calcium 916 86 1.107(0.979–1.252) 1.090(0.943–1.259) Low Magnesium low calcium 1780 338 1.353(1.283–1.427) 1.237(1.142–1.339) Multiplicative interaction: OR(95%CI) = 1.691(1.405–2.035) P < 0.01 OR a univariate analyses. OR e adjusted for weight gain during pregnancy, mother's BMI, total energy intake, monthly income per capita, maternal education level, smoking, maternal employ, multivitamin supplement, gestational hypertension, history of premature birth, reproductive history and dietary Magnesium intake. Interaction effects of maternal dietary magnesium intake, calcium supplements and dietary calcium intake on the risk of PTB As shown in interaction effects of maternal dietary magnesium intake、calcium supplements and dietary calcium intake on the risk of PTB (Table 6 ), in the preconception and second trimester groups, the intake of magnesium, calcium, and calcium supplements was not significantly associated with the risk of PTB. However, in the first trimester and third trimester groups, regardless of whether calcium supplements were used or not, the group with low calcium and magnesium intake had a significantly increased risk of PTB. Specifically, for the first trimester (OR = 1.085, 95% CI: 1.011–1.165), and for the third trimester (OR = 1.106, 95% CI: 1.028–1.189), and for the first trimester (OR = 1.073, 95% CI: 1.022–1.126), and for the third trimester(OR = 1.113, 95% CI: 1.057–1.172). Moreover, there was a multiplicative interaction effect in all four pregnancy periods, showed a relatively significant risk of PTB during the first trimester(OR = 1.063, 95% CI: 1.001 − 1.128). Table 6 Interaction effects of maternal dietary Magnesium intake、Calcium supplements and dietary Calcium intake on the risk of PTB Maternal dietary intake Calcium supplements Users Nonusers term preterm OR f (95%CI) term preterm OR f (95%CI) Preconception High calcium and high Magnesium 157 13 1.000 4612 387 1.158(0.810–1.656) High calcium and low Magnesium 17 1 0.443(0.028–7.097) 385 37 1.009(0.712–1.429) Low calcium and high Magnesium 19 4 1.314(0.843–2.047) 1185 166 1.072(0.947–1.215) Low calcium and low Magnesium 33 4 0.765(0.486–1.205) 1609 268 1.092(0.979–1.218) Multiplicative interaction: OR(95%CI) = 1.112(1.043–1.187) P = 0.0013 First pregnancy High calcium and high Magnesium 2461 185 1.000 2042 181 1.015(0.893–1.153) High calcium and low Magnesium 413 36 0.937(0.585–1.501) 293 25 0.930(0.778–1.113) Low calcium and high Magnesium 589 57 0.963(0.873–1.062) 448 74 1.063(1.001–1.128) Low calcium and low Magnesium 897 149 1.085(1.011–1.165) 874 173 1.073(1.022–1.126) Multiplicative interaction: OR(95%CI) = 1.168(1.089–1.254) P < 0.001 Second Trimester High calcium and high Magnesium 1825 126 1.000 1687 148 1.042(0.897–1.210) High calcium and low Magnesium 1053 87 1.070(0.712–1.613) 639 61 0.999(0.857–1.165) Low calcium and high Magnesium 228 24 0.922(0.789–1.079) 217 30 1.023(0.931–1.123) Low calcium and low Magnesium 1254 190 1.064(0.973–1.163) 1114 214 1.061(0.999–1.127) Multiplicative interaction: OR(95%CI) = 1.133(1.047–1.225) P = 0.0019 Third Trimester High calcium and high Magnesium 2510 179 1.000 2072 172 1.020(0.896–1.161) High calcium and low Magnesium 546 51 1.199(0.781–1.841) 370 35 1.107(0.864–1.197) Low calcium and high Magnesium 390 44 1.013(0.906–1.132) 349 61 1.065(0.995–1.139) Low calcium and low Magnesium 914 153 1.106(1.028–1.189) 866 185 1.113(1.057–1.172) Multiplicative interaction: OR(95%CI) = 1.287(1.192–1.389) P < 0.001 OR f adjusted for weight gain during pregnancy,Mother's BMI, Mother's age,Gestational diabetes,total energy intake, monthly income per capita, maternal education level, smoking, maternal employ, multivitamin supplement, gestational hypertension, history of premature birth, reproductive history. Discussion In this nested cohort study, we observed a significantly increased risk of preterm labor in women with low dietary calcium intake before and during pregnancy, demonstrating a dose - response relationship, The data similarly demonstrate that insufficient magnesium intake during both the second and third trimesters is associated with an elevated risk of PTB, while inadequate calcium supplements in third trimester further compounds this risk. And there is a multiplicative interaction among the three. This is the first comprehensive study to investigate the effects of dietary magnesium, calcium, and calcium supplements intakes on PTB from preconception to the entire pregnancy. Before conducting another study, the research on the relationship between dietary magnesium and calcium during the perinatal period and calcium supplements intake, as well as PTB, is still limited. There are many factors influencing premature birth, among which the influence of uterine contractions on premature birth has received extensive attention. The uterine muscle layer is composed of smooth muscle tissue, and smooth muscle tissue undergoes various physiological changes, such as hypertrophy, hyperplasia, contraction and cell apoptosis, which are very important for uterine activity. Calcium is a key regulatory factor in the contraction mechanism of smooth muscle tissue, and there are many well-defined and clinically used agonists and antagonists of uterine smooth muscle pathways, such as Ca2 + channel blockers [ 21 – 23 ] . β-adrenergic receptor agonists (ß-agonists) bind to β-adrenergic receptors. The β-adrenergic receptors are coupled to G proteins, which activate adenylate cyclase, converting triphosphate adenosine into cAMP. An increase in cAMP activates PKA, which phosphorylates L-type calcium channels, thereby leading to an increase in calcium entering the cells. The transmembrane calcium flux is an important regulator of intracellular calcium, initiating a series of events, including the interaction of myosin light chain kinase-regulated contractile proteins (myosin and actin), ultimately resulting in muscle contraction [ 24 – 25 ] Magnesium is an essential element for the normal functioning of the body. It participates in many metabolic pathways within cells and acts as a stabilizer for cell membranes, reducing their permeability. Magnesium is responsible for facilitating the transport of electrolytes across cell membranes to maintain homeostasis within the body. Magnesium can stabilize DNA molecules and also maintain tRNA, which is involved in normal muscle contraction, neuronal excitation, and the release of neurotransmitters [ 26 – 28 ] . Magnesium has a relaxing effect on smooth muscles, so it is used as an inhibitor of uterine contractions in premature births, and it acts as a calcium antagonist. At the physiological level, uterine contractions are inhibited by extracellular Mg 2+ , and it is reported that Mg 2+ inhibits spontaneous depolarization. Therefore, Mg 2+ is used for treating uterine contractions in premature births [ 29 – 32 ] . Another important element in maintaining the myometrial relaxation is a correct balance between ROS and NO productions. Indeed, when ROS production exceeds the myometrial antioxidant scavenging capacity, oxidative stress may increase due to consequent cellular dysfunction and tissue damage. Recently, there has also been a great deal of interest in the relaxing effect of NO on the uterine muscle layer. Therefore, NO relaxes the uterine muscle layer by increasing Mg and inhibiting Ca 2+ . Research reports on the mechanism of magnesium in inhibiting the contraction of the uterine muscle layer state that it rapidly induces dose-dependent inhibition of Ca 2+ uptake. The researchers concluded that this inhibition of calcium uptake is the reason for magnesium's inhibitory effect on spontaneous uterine muscle layer contractions [ 33 – 35 ] . Magnesium is crucial for bone development, stimulating the activity of phosphatases and osteoblasts, which are enzymes involved in bone formation. Magnesium deficiency directly affects bone density. Animal studies have shown that a low calcium intake can lead to osteoporosis. Animals deficient in magnesium have slender and fragile bones with severe degradation of mechanical strength. Magnesium deficiency affects the skeleton by influencing the main regulatory factors of calcium homeostasis - PTH and 1, 25(OH)2 D3 [ 36 – 39 ] . Most studies suggest that adequate magnesium intake during pregnancy can reduce the risk of PTB. A review article from the United States found that the results of 11 observational studies all indicated a negative correlation between serum magnesium levels and the incidence of PTB [ 9 ] . In the review titled "Study Based on the Alliance Between Serum magnesium Levels and Preterm Labor", Deeksha HS conducted a case-control study to determine the relationship between magnesium levels and preterm labor. The case-control study concluded that the magnesium levels of pregnant women with preterm labor were lower than those of women with full-term pregnancies [ 40 ] . In a study, the results indirectly indicated that magnesium has a significant impact on the duration of pregnancy for pregnant women [ 41 ] . During pregnancy, the demand for magnesium by pregnant women increases. However, most pregnant women cannot meet this increased demand. Magnesium intake during pregnancy has an impact on both the mother and the newborn's health, including fetal growth restriction and PTB [ 42 ] . Dietary habits may lead to deficiencies (including calcium) and have negative impacts on the health of mothers and their fetuses/newborns [ 43 ] . Calcium intake during the third trimester of pregnancy is of vital importance for fetal skeletal development. The recommended dietary intake of calcium for pregnant women is 1000 mg per day [ 44 ] . Some studies also suggest that pregnant women should consume 1.5 g − 2 g of calcium daily before giving birth [ 45 ] . In this study, it was found that a calcium intake lower than 359 mg per day would increase the risk of PTB. Calcium supplements during pregnancy can reduce the risk of PTB and preeclampsia in pregnant women with low dietary calcium intake [ 46 – 47 ] . Calcium supplements can prevent the occurrence of PTB. The average risk of PTB in the calcium supplements group was reduced (11 trials, 15275 women; RR = 0.76, 95%CI 0.60 to 0.97; I²=60%; low-quality evidence) [ 48 ] . A study from China indicates that the supplementation of trace elements by pregnant women in the northwest region of China is lower than that recommended by Chinese guidelines and also lower than the standards recommended by WHO [ 49 ] . In this study, the number of pregnant women taking calcium supplements during pregnancy was relatively small. In the perspective of pregnant women, it is necessary to take folic acid and iron supplements during pregnancy. However, few people think that magnesium and calcium supplements should also be taken. In the future, pregnant women should be encouraged to pay attention to dietary consultation during pregnancy and to take necessary vitamins and trace elements supplements, so as to reduce the risk of PTB and other adverse pregnancy outcomes. In our research, we strictly ensured the quality throughout the entire process from questionnaire design to data entry and data calculation, in order to reduce recall bias and guarantee the accuracy of the calculation results. However, there are still several limitations that need to be acknowledged. Firstly, we cannot quantitatively analyze the interactions among various vitamins and trace elements in the diet. There might be potential confounding factors, although we have included the common confounding factors. Secondly, we cannot determine the calcium supplements intake. But, according to our research, pregnant women can use the dietary magnesium intake of first trimester(359.193–583.690) mg/d, second trimester(369.733–603.250) mg/d, third trimester(365.228-908.135) mg/d and the dietary calcium intake of preconception(443.608-1074.897) mg/d, first trimester(629.253-1091.939) mg/d, second trimester(674.119-1205.243) mg/d, third trimester(678. 187–2493. 333) mg/d to prevent the occurrence of PTB risk. Conclusions Our research indicates that, firstly, low dietary magnesium intake during the third trimester of pregnancy will increase the risk of PTB, and the absence of calcium supplements during the third trimester will also increase the risk of PTB. Secondly, insufficient dietary calcium intake before and after pregnancy will both increase the risk of PTB. Our research also found that there is a synergistic effect between magnesium and calcium intake on the risk of PTB (preconception, during pregnancy, first trimester, second trimester, and third trimester), and there is also a synergistic effect between magnesium, calcium and calcium supplements on the risk of PTB (preconception and third trimester). These results suggest that moderate increases in magnesium, calcium and calcium supplement intake before and during pregnancy are important for reducing the incidence of PTB in Lanzhou, Gansu Province, In the future, studies should be conducted on maternal biomarkers, minerals, macroelements, other trace elements and genetic data to confirm these findings and explain the underlying mechanisms. Abbreviations PTB: Preterm birth OR: Odds ratio 95% CI: 95% confidence interval RCS: Multivariate-adjusted restricted cubic spline FFQ: Semi-quantitative food frequency questionnaire RNI: Recommended nutrient intake Non-PTB: delivery at or beyond 37 weeks of gestation (full-term delivery) BMI: Body mass index Declarations Availability of data and materials The datasets generated and/or analyzed during the current study are not made public as they contain private information of the women. However, they can be obtained from the corresponding author upon reasonable request. Fundings This work was supported in part by The Science and Technology Department Grant of Lanzhou City (No.2022-5-85), and Gansu Provincial Health Commission Research Project (No.GSWSKY2024-14; GSWSKY2024-49), and the Traditional Chinese Medicine Management Project of Gansu Province (No.GZKG-2024-43). Authors' information Zifu Wang ¹ ,²† , Lei Cao ² ,³† , Yuqing Li ² ,³ , Chenyan Yang ² ,³ , Baohong Mao ³ ,² , Liping Yang ¹ ,² , Yue Fang ⁴ ¹ Department of Public Health and Infection Management, Gansu Provincial Hospital of Traditional Chinese Medicine, Lanzhou 730000, Gansu Province, China. ² School of Public Health, Gansu University of Chinese Medicine, Lanzhou 730000, Gansu Province, China. ³ Department of Medical Education, Gansu Provincial Maternity and Child-care Hospital (Gansu Provincial Central Hospital), Lanzhou 730050, Gansu Province, China. ⁴ Department of Planning and Development, Gansu Provincial Hospital of Traditional Chinese Medicine, Lanzhou 730000, Gansu Province, China. † :These authors contributed equally to this work. Corresponding Author: Baohong Mao , Liping Yang, Yue Fang Lanzhou 730050, Gansu Province, China. Lanzhou 730000, Gansu Province, China. Email address: [email protected] [email protected] [email protected] Ethics declarations Ethical approval and consent to participate Informed consent was obtained from study participants. This research approved by Medical Ethics Committee of Gansu Provincial Maternity and Child-care Hospital [2018] The Ethics Committee of Gansu Provincial Maternity and Child-care Hospital No.(29). Consent to Participate declaration All the participants in the study have fully understood the research content, potential risks and benefits, and have voluntarily agreed to take part in the study. Consent for publication Not Applicable. Competing interests The authors declare that they have no competing interests. References Ohuma EO, Moller AB, Bradley E, Chakwera S, Hussain-Alkhateeb L, Lewin A, Okwaraji YB, Mahanani WR, Johansson EW, Lavin T, Fernandez DE, Domínguez GG, de Costa A, Cresswell JA, Krasevec J, Lawn JE, Blencowe H, Requejo J, Moran AC. 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BMJ Glob Health. 2023 Jan;8(Suppl 2):e010992. doi: 10.1136/bmjgh-2022-010992. PMID: 36717156; PMCID: PMC9887708. Atallah AN, Hofmeyr GJ, Duley L. calcium supplements during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database Syst Rev. 2002;(1):CD001059. doi:10. 1002/14651858. CD001059 Hofmeyr GJ, Lawrie TA, Atallah ÁN, Torloni MR. calcium supplements during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database Syst Rev. 2018 Oct 1;10(10):CD001059. doi: 10. 1002/14651858. CD001059. pub5. PMID: 30277579; PMCID: PMC6517256. Liu D, Cheng Y, Dang S, Wang D, Zhao Y, Li C, Li S, Lei F, Qu P, Mi B, Zhang R, Li J, Zeng L, Yan H. Maternal adherence to micronutrient supplementation before and during pregnancy in Northwest China: a large-scale population-based cross-sectional survey. BMJ Open. 2019 Aug 8;9(8):e028843. doi: 10. 1136/bmjopen-2018-028843. PMID: 31399455; PMCID: PMC6701669. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7305270","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":502145616,"identity":"1e97f2bd-ad83-40e6-9b30-52956aa22fed","order_by":0,"name":"Zifu Wang","email":"","orcid":"","institution":"Gansu Provincial Hospital of Traditional Chinese Medicine","correspondingAuthor":false,"prefix":"","firstName":"Zifu","middleName":"","lastName":"Wang","suffix":""},{"id":502145619,"identity":"fa16651f-427a-4d5c-8c7d-a9257eec0665","order_by":1,"name":"Lei Cao","email":"","orcid":"","institution":"Gansu University of Chinese Medicine","correspondingAuthor":false,"prefix":"","firstName":"Lei","middleName":"","lastName":"Cao","suffix":""},{"id":502145622,"identity":"fc50d8b8-05ac-4be2-8833-191f15fd6d08","order_by":2,"name":"Yuqing Li","email":"","orcid":"","institution":"Gansu University of Chinese Medicine","correspondingAuthor":false,"prefix":"","firstName":"Yuqing","middleName":"","lastName":"Li","suffix":""},{"id":502145623,"identity":"10453031-a67a-4295-8ac7-31869bc31c92","order_by":3,"name":"Chenyan Yang","email":"","orcid":"","institution":"Gansu University of Chinese Medicine","correspondingAuthor":false,"prefix":"","firstName":"Chenyan","middleName":"","lastName":"Yang","suffix":""},{"id":502145624,"identity":"2fc3a45a-ebf1-4081-8723-6e2e081a4fa2","order_by":4,"name":"Baohong Mao","email":"","orcid":"","institution":"Gansu Provincial Maternity and Child-care Hospital (Gansu Provincial Central Hospital)","correspondingAuthor":false,"prefix":"","firstName":"Baohong","middleName":"","lastName":"Mao","suffix":""},{"id":502145625,"identity":"40eb7e79-25b8-477a-ba35-48ebb565736b","order_by":5,"name":"Liping Yang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAklEQVRIiWNgGAWjYBACPmYGhgNQNuMDKMMArxY2JC3MMKUEtCCzJYjTws578HDBL4bE/tnt1yq//KlLbGBv3ibBUHMHj8P4Eg7P7GNInHHnTNlt2Ta2xAaeY2USDMee4dHCY3CYt4chseFGTtptyQaexAaJHDMJxobDhLXMB2oplvgjkdgg/4YILTw/GBI33Eg/xviBzQBoCw8hLUC/8DZIGG+8kcMszdiWYNzGk1ZskXAMtxZ+/rOHP/P8sZGddyP94ccff+pk+9kPb7zxoQa3FgYGHmC0t0k4NjDwGDAD2Y5tIMEEPBrAWhj+MNgzMLA/YPzBAGKMglEwCkbBKEAFAPJYU/+b1huWAAAAAElFTkSuQmCC","orcid":"","institution":"Gansu Provincial Hospital of Traditional Chinese Medicine","correspondingAuthor":true,"prefix":"","firstName":"Liping","middleName":"","lastName":"Yang","suffix":""},{"id":502145626,"identity":"e956276e-3511-4075-813c-4494f8ba1003","order_by":6,"name":"Yue Fang","email":"","orcid":"","institution":"Gansu Provincial Hospital of Traditional Chinese Medicine","correspondingAuthor":false,"prefix":"","firstName":"Yue","middleName":"","lastName":"Fang","suffix":""}],"badges":[],"createdAt":"2025-08-06 03:38:30","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7305270/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7305270/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":89562996,"identity":"3624d616-4ea9-4ad2-8f51-622c704e8f02","added_by":"auto","created_at":"2025-08-21 10:29:00","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1250596,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-7305270/v1/b220d0fa31437ef1162e40e0.png"},{"id":89560964,"identity":"5e3e3c31-5dfe-4e7d-bcdd-311a98217c33","added_by":"auto","created_at":"2025-08-21 10:21:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1306112,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-7305270/v1/9599d464a0de9ec42c7766d7.png"},{"id":89565469,"identity":"deefe64d-f9a4-4f69-912c-f897b21a12eb","added_by":"auto","created_at":"2025-08-21 10:45:07","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4299805,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7305270/v1/6ea3983d-87e0-4452-86db-fe4ca396611b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Maternal Intake of Magnesium, Calcium, and Calcium Supplements: Association with Preterm Birth Risk in a Nested Case-Control Study","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAccording to WHO criteria, PTB refers to delivery prior to 37 weeks of pregnancy\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e. PTB is the second largest direct cause of child deaths in children younger than 5 years, and PTB affects both high-income and low-to-middle-income countries, with incidence rates ranging from 5\u0026ndash;18%, of which approximately 60% occur in low-and middle-income countries\u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. Epidemiological data compiled from a Chinese systematic review established the national PTB rate to be 5%\u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e. PTB constitutes a major determinant of adverse neonatal outcomes and mortality\u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. PTB is associated with increased risks of respiratory distress syndrome, cerebral palsy, and other developmental disorders. Moreover, preterm infants may face elevated susceptibility to certain chronic non-communicable diseases in later life\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. Studies have demonstrated that maintaining optimal nutrition throughout gestation plays a pivotal role in mitigating adverse obstetric outcomes and ensuring long-term maternal and fetal well-being\u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e. Adequate maternal nutritional intake and improved health status preconception and during gestation positively influence fetal growth and development, optimize pregnancy outcomes, and increase perinatal survival rates\u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. Deficiencies in trace elements are prevalent during both preconception and pregnancy periods, necessitating increased dietary intake of essential micronutrients\u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e. Evidence suggests that magnesium modulates uterine smooth muscle activity, indicating that maternal magnesium intake may influence gestational duration. However, current literature remains limited regarding the association between magnesium supplementation and PTB risk\u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e Magnesium therapy demonstrates neuroprotective effects during the perinatal period and shows particular efficacy in preventing neurological damage in preterm infants\u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e. Magnesium is an essential micronutrient involved in numerous physiological processes, including muscular relaxation, skeletal development, electrolyte homeostasis, and blood pressure regulation. Given these critical functions, maintaining adequate magnesium status during pregnancy is of paramount importance. However, achieving optimal magnesium supplementation in the prenatal period presents significant clinical challenges, despite the availability of multiple intake modalities\u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e. Calcium deficiency augments myometrial contractility by modulating muscular cell tension, consequently triggering preterm labor\u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e. Evidence indicates widespread calcium insufficiency among pregnant women in low- and middle-income countries. Systematic reviews demonstrate that calcium supplements during pregnancy significantly reduces pregnancy-related complications, including pre-eclampsia, maternal morbidity and PTB. While WHO recommends a daily calcium intake of 1.5g-2g for pregnant women, emerging evidence suggests that 1g/day may achieve comparable clinical benefits in certain populations\u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e. Population-based studies reveal a high prevalence of inadequate dietary calcium intake (85.9%). Maternal calcium supplements during gestation demonstrates a significant inverse association with PTB risk\u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e. Current evidence remains limited regarding the associations between magnesium/calcium status and PTB risk. Even fewer studies have examined the combined effects of magnesium and calcium supplements, with virtually no research investigating the potential synergistic interactions among these micronutrients in relation to PTB.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eStudy population\u003c/h2\u003e\u003cp\u003eA birth cohort study was conducted from January 2018 to June 2019 at the largest hospital of its kind in Lanzhou City, Gansu Province. Eligible participants were pregnant women aged 18 years or older, without a history of mental illness, who received regular prenatal care and provided written informed consent. The study included a total of 8897 eligible women, comprising 880 who delivered preterm infants and 8017 who delivered at term. The study protocol was approved by the Institutional Review Board of the Maternal and Child Health Hospital of Gansu Province [2018 (029)], and all participants provided written informed consent\u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eDietary surveys, magnesium, calcium and calcium supplements daily intake\u003c/h3\u003e\n\u003cp\u003eDaily surveys and dietary magnesium, calcium and calcium supplements were collected through a face-to-face semi-quantitative food frequency questionnaire (FFQ)\u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e. The survey covered sociological characteristics, disease history, physiological fertility, and dietary intake. Dietary status was assessed using a 24-hour dietary recall survey conducted by trained medical staff. Participants reported the types and quantities of all foods consumed over three consecutive days, covering 12 main categories: cereals, oils and fats, vegetables, fruits, poultry, livestock meat and its products, eggs, aquatic products, beans and soy products, milk and milk products, bacteria and algae, snacks and drinks, as well as 59 other common food items. After obtaining the informed consent from the patients, four dietary and nutritional surveys were conducted on all the research subjects. The first survey was carried out during the 3-month period preconception when they came to the hospital for preconception consultation and health check-ups. The other three surveys were conducted during the early pregnancy (\u0026le;\u0026thinsp;13 weeks of gestation), the middle pregnancy (14\u0026ndash;27 weeks of gestation), and the late pregnancy (\u0026ge;\u0026thinsp;28 weeks of gestation) when they came to the hospital for prenatal check-ups. After completing all dietary surveys, the daily intake of dietary vitamins and trace elements of each pregnant woman during different pregnancies was calculated following the second edition of the Chinese Food Composition Table\u0026nbsp;2009\u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e Daily vitamin and trace element intakes in different pregnancies were divided into groups based on the recommended nutrient intake (RNI) of Chinese residents\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e for statistical analysis. The RNI is the amount of a nutrient that is enough to ensure that the needs of 97. 5% of the population are met. Data on pregnancy-related complications and birth outcomes were extracted from medical records.\u003c/p\u003e\n\u003ch3\u003ePreterm Labor\u003c/h3\u003e\n\u003cp\u003ePreterm labor (PTB) is defined as a live birth occurring before the completion of 37 weeks of gestation, and such cases were included in the case group for analysis. Non-PTB, defined as delivery at or beyond 37 weeks of gestation (full-term delivery), was included in the control group for analysis. Deliveries were further stratified into three categories: \u0026lt;32 weeks, ≦32\u0026thinsp;\u0026lt;\u0026thinsp;34 weeks, and ≦\u0026thinsp;34\u0026thinsp;\u0026lt;\u0026thinsp;37 weeks.\u003c/p\u003e\n\u003ch3\u003eBody mass index (BMI) and gestational weight gain\u003c/h3\u003e\n\u003cp\u003ePreconception weight was self-reported during the first prenatal care visit. BMI was calculated as weight (kg) divided by the square of height (m), and then subcategorized in accordance with the Working Group of Obesity in China as follows: underweight (BMI\u0026thinsp;\u0026lt;\u0026thinsp;18. 5 kg/m2), normal weight (18. 5 kg/m2\u0026thinsp;\u0026le;\u0026thinsp;BMI\u0026thinsp;\u0026lt;\u0026thinsp;24 kg/m2), overweight (24 kg/m2\u0026thinsp;\u0026le;\u0026thinsp;BMI\u0026thinsp;\u0026lt;\u0026thinsp;28 kg/m2), and obesity (BMI\u0026thinsp;\u0026ge;\u0026thinsp;28 kg/m2). Gestational weight gain in kg was calculated by subtracting pre-pregnancy weight from maternal weight at delivery, which was categorized based on the US Institute of Medicine (IOM) GWG Guidelines 2009\u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003eCovariates\u003c/h3\u003e\n\u003cp\u003eThe study covariates included maternal age, body mass index (BMI) during pregnancy, maternal education level, household income per capita, alcohol consumption during pregnancy, smoking status during pregnancy (active and passive smoking), maternal employment status (employed during pregnancy, never employed, or not employed only during pregnancy), presence of gestational hypertension, history of PTB, presence of gestational diabetes mellitus, parity (primipara or multipara), and neonatal sex.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eStatistical analysis\u003c/h2\u003e\u003cp\u003eComparisons of the selected characteristics between women with PTB and Non-PTB were evaluated using the chi-square test or Fisher's exact test. The differences in measurement data between the two groups were analyzed by independent-sample t test, and the variables that did not meet the normal distribution were compared between groups by the Wilcoxon rank-sum test. Unconditional logistic regression was used to determine the odds ratios (ORs) and 95% confidence intervals (CIs) for the association between dietary magnesium, calcium and calcium supplements intake and the risk of PTB and its clinical subtypes. Confounding factors, including weight gain during pregnancy, maternal BMI, total energy intake, monthly income per capita, maternal education level, smoking, maternal employment, multivitamin supplementation, gestational hypertension, history of PTB, and reproductive history, were adjusted for in the unconditional logistic regression models. Dietary magnesium and calcium intake were categorized into quartiles, and the dose\u0026ndash;response relationship (P for trend) was calculated based on those categorical levels. The association between dietary magnesium, calcium and calcium supplements intake and the risk of PTB may result in a nonlinear correlation. Multivariate-adjusted restricted cubic spline (RCS) models with three knots were applied to explore the nonlinear association. The number of knots was determined by comparing the criteria between Bayesian and Akaike information. The RCS models were adjusted for the potential confounding factors listed above. The multiplicative interaction parameters [OR\u0026thinsp;=\u0026thinsp;OR11/(OR01 \u0026times; OR10)] and 95% CI were also estimated by including the abovementioned variables\u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. Cut-off values for magnesium and calcium were determined for four gestational periods (preconception, first trimester, second trimester, and third trimester) using SPSS version 26 for windows, We estimated 95% CI for each of these measures; the null values of RERI and AP were 0, whereas the null value for S was 1. All statistical tests were two-sided. Analyses were performed using SAS 9. 4 (SAS Institute, Inc, Cary, NC, USA). The RCS models were performed by R software, version 4. 4. 2(package 'Hmisc', 'rms', and 'survival').\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003eBasic characteristics of the study population\u003c/h2\u003e\u003cp\u003eA total of 8897 eligible women participated, including 880 who delivered preterm infants and 8017 who delivered at term. As illustrated in distributions of selected characteristics of the study population (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), mothers of preterm infants, compared to those of Non-PTB infants, exhibited lower household monthly income, lower educational attainment, reduced employment rates, higher prevalence of gestational hypertension, increased smoking rates, and a greater likelihood of gestational diabetes, history of PTB, and multiparity. Additionally, mothers in the case group exhibited significantly lower maternal weight gain and reduced total energy intake compared to the control group. However, no significant differences were observed between the two groups regarding alcohol consumption during pregnancy or neonatal sex.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eDistributions of selected characteristics of the study population\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCharacteristics\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003epreterm(n\u0026thinsp;=\u0026thinsp;880)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eterm(n\u0026thinsp;=\u0026thinsp;8017)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003eχ\u0026sup2;\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eP-value\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMaternal age\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e75.813\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026lt;23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e110(1.24)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e504(5.66)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e23\u0026le; ~ \u0026lt;26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e135(1.52)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1192(13.40)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e26\u0026le; ~ \u0026lt;30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e270(3.03)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3453(38.81)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026ge;30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e365(4.10)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2868(32.24)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003epregnancy BMI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e7.693\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.021\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026lt;18.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e176(1.98)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1709(19.21)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e18.5\u0026le; ~ \u0026lt;24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e583(6.55)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e5450(61.26)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBMI\u0026thinsp;\u0026ge;\u0026thinsp;24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e121(1.36)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e858(9.64)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMaternal education level\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e179.736\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026le;middle school\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e333(3.74)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1577(17.73)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003emiddle school\u0026lt; ~ \u0026le;Community college\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e340(3.82)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3215(36.14)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026ge;college\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e207(2.33)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3225(36.25)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ehousehold income per capita\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e88.84\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026le;2000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e340(3.82)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1945(21.86)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2000\u0026lt; ~ \u0026le;5000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e476(5.35)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e5171(58.12)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026gt;5000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e64(0.72)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e901(10.13)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDrink during pregnancy\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.723\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.189\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eyes\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3(0.03)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e12(0.013)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eno\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e877(9.86)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8805(89.97)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSmoking(passive smoke,active smoke)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e7.853\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.005\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eyes\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e209(2.35)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e6433(72.31)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eno\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e671(7.54)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1584(17.80)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMaternal employment status\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e51.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eemployed during pregnancy\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e381(4.28)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4432(49.81)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003enever employed\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e357(4.01)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2384(26.80)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNot employed only during pregnancy\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e142(1.60)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1201(13.50)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGestational hypertension\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e267.887\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eyes\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e142(1.60)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e291(3.27)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eno\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e738(8.29)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7726(86.84)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHistory of premature birth\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e138.781\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eyes\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e62(0.70)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e107(1.20)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eno\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e818(9.19)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7910(88.91)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGestational diabetes\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e4.89\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.027\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eyes\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e15(0.17)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e74(0.83)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eno\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e865(9.72)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7943(89.28)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eChildbearing history\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e60.898\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePrimipara\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e549(6.17)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e5983(67.25)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMultipara\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e331(3.72)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2043(22.86)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNeonatal sex\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.498\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.481\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMale\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4103(51.18)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e443(50.34)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFemale\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3726(46.48)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e382(43.41)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMissing\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e188(2.34)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e55(6.25)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eAssociations of maternal dietary magnesium intake with the risk of PTB\u003c/h2\u003e\u003cp\u003eAs shown in associations of maternal dietary magnesium intake with the risk of PTB\u003c/p\u003e\u003cp\u003e(Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), preconception group with low magnesium intake had a significantly increased risk of PTB (OR\u0026thinsp;=\u0026thinsp;1.589, 95% CI: 1.372\u0026ndash;1.841). The risk of PTB decreased after each increase of one quartile interval. After adjusting for confounding factors, the risk of PTB still increased (OR\u0026thinsp;=\u0026thinsp;1.107, 95% CI: 0.916\u0026ndash;1.339). The first trimester was almost the same as preconception. In the subgroup of the second trimester with low magnesium intake, the risk of low magnesium intake group was significantly increased in subgroup 32\u0026thinsp;\u0026le;\u0026thinsp;weeks\u0026thinsp;\u0026lt;\u0026thinsp;34 (OR\u0026thinsp;=\u0026thinsp;1.411, 95% CI: 0.910\u0026ndash;2.187), and the risk decreased by 1.262 (1.019\u0026ndash;1.562) after each increase of one quartile interval (P for trend\u0026thinsp;=\u0026thinsp;0.0328). In the third trimester subgroup with low magnesium intake, the risk of PTB was almost the same as that in the second trimester. (Fig.\u0026nbsp;1) Restricted cubic spline models of PTB risk associated with magnesium intake preconception (A), at the first trimester (B), at the second trimester (C), and at the third trimester (D), illustrates the RCS curve of dietary magnesium intake preconception and during pregnancy PTB risk. As daily magnesium intake increases, the risk of PTB decreases and then stabilizes. When intake is at first trimester(359.193\u0026ndash;583.690) mg/d, second trimester(369.733\u0026ndash;603.250) mg/d, third trimester(365.228-908.135) mg/d, magnesium may serve as a protective factor against PTB.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eAssociations of maternal dietary Magnesium intake with the risk of PTB\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"12\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" morerows=\"1\" nameend=\"c2\" namest=\"c1\" rowspan=\"2\"\u003e\u003cp\u003eDietary Magnesium intake(mg/d)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eTerm\u003c/p\u003e\u003cp\u003e(8017)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003ePreterm\u003c/p\u003e\u003cp\u003e(\u0026lt;\u0026thinsp;37weeks)\u003c/p\u003e\u003cp\u003ecases(880)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eOR\u003csub\u003ea\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eOR\u003csub\u003eb\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;32weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e32\u0026thinsp;\u0026le;\u0026thinsp;weeks\u0026thinsp;\u0026lt;\u0026thinsp;34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e34\u0026thinsp;\u0026le;\u0026thinsp;weeks\u0026thinsp;\u0026lt;\u0026thinsp;37\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003en\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eOR\u003csub\u003eb\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003en\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003eOR\u003csub\u003eb\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003en\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003eOR\u003csub\u003eb\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003ePreconception\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026ge;222.1193\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5973\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e570\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e102\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e372\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;222.1193\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2044\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e310\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.589(1.372\u0026ndash;1.841)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.038(0.858\u0026ndash;1.255)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e66\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.242(0.832\u0026ndash;1.855)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e68\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.326(0.886\u0026ndash;1.986)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e176\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.909(0.718\u0026ndash;1.151)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePer interquartile increase\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.212(1.138\u0026ndash;1.291)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.016(0.923\u0026ndash;1.119)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.961(0.777\u0026ndash;1.189)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.044(0.848\u0026ndash;1.285)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.022(0.908\u0026ndash;1.150)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e for trend\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.7462\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.7132\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.6842\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.7223\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eFirst trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026ge;293.3383\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5540\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e497\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e89\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e327\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;293.3383\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2477\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e383\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.724(1.496\u0026ndash;1.985)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.124(0.932\u0026ndash;1.356)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.279(0.858\u0026ndash;1.906)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.305(0.877\u0026ndash;1.943)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e221\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.046(0.830\u0026ndash;1.319)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePer interquartile increase\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.266(1.188\u0026ndash;1.349)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.036(0.943\u0026ndash;1.137)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.084(0.882\u0026ndash;1.332)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.090(0.892\u0026ndash;1.332)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.011(0.902\u0026ndash;1.134)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e for trend\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.4627\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.4430\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.3994\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.8492\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eSecond trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026ge;354.0812\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3957\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e328\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e220\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;354.0812\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4060\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e552\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.640(1.421\u0026ndash;1.893)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.146(0.938\u0026ndash;1.399)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e108\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.080(0.692\u0026ndash;1.683)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e116\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.411(0.910\u0026ndash;2.187)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e328\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.095(0.858\u0026ndash;1.397)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePer interquartile increase\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.272(1.193\u0026ndash;1.355)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.039(0.943\u0026ndash;1.143)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.008(0.815\u0026ndash;1.246)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.262(1.019\u0026ndash;1.562)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.991(0.881\u0026ndash;1.116)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e for trend\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.4438\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.9411\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.0328\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.8868\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eThird trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026ge;309.5003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5321\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e456\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e65\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e81\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e310\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;309.5003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2696\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e424\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.835(1.595\u0026ndash;2.111)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.267(1.043\u0026ndash;1.541)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.830(1.182\u0026ndash;2.832)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e89\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.341(0.886\u0026ndash;2.029)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e238\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.143(0.899\u0026ndash;1.453)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePer interquartile increase\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.316(1.235\u0026ndash;1.404)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.102(1.000-1.215)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.274(1.020\u0026ndash;1.591)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.221(0.988\u0026ndash;1.509)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.026(0.911\u0026ndash;1.155)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e for trend\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.0504\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.0329\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.0641\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.6717\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"12\" nameend=\"c12\" namest=\"c1\"\u003e\u003cp\u003eOR\u003csub\u003ea\u003c/sub\u003e univariate analyses.\u003c/p\u003e\u003cp\u003eOR\u003csub\u003eb\u003c/sub\u003e adjusted for weight gain during pregnancy,Mother's BMI, Mother's age,Gestational diabetes,total energy intake, monthly income per capita, maternal education level, smoking, maternal employ, multivitamin supplement, gestational hypertension, history of premature birth, reproductive history, dietary calcium intake and Supplement calcium.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eAssociations of maternal dietary calcium intake with the risk of PTB\u003c/h2\u003e\u003cp\u003eAs shown in associations of maternal dietary calcium intake with the risk of PTB (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), the risk of PTB was significantly increased in the group with low calcium intake preconception (OR\u0026thinsp;=\u0026thinsp;1.834, 95% CI: 1.594\u0026ndash;2.109). The risk decreased after each increase of one quartile interval (OR\u0026thinsp;=\u0026thinsp;1.306, 95% CI: 1.225\u0026ndash;1.393, P for trend\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). After adjusting for confounding factors, the risk still increased, and it decreased after each increase of one quartile interval. Moreover, in subgroup 34\u0026thinsp;\u0026le;\u0026thinsp;weeks\u0026thinsp;\u0026lt;\u0026thinsp;37, the risk of PTB in the group with low calcium intake was more significant (OR\u0026thinsp;=\u0026thinsp;1.390, 95% CI: 1.113\u0026ndash;1.736), and the risk decreased after each increase of one quartile interval (OR\u0026thinsp;=\u0026thinsp;1.154, 95% CI: 1.029\u0026ndash;1.294, P for trend\u0026thinsp;=\u0026thinsp;0.0145). The results of the first trimester, second trimester, and third trimester were almost the same as those preconception. (Fig.\u0026nbsp;2) Restricted cubic spline models of PTB risk associated with calcium intake preconception (A), at the first trimester (B), at the second trimester (C), and at the third trimester (D), illustrates the RCS curve of dietary calcium intake preconception and during pregnancy PTB risk. As daily calcium intake increases, the risk of PTB decreases and then stabilizes. When the intake levels are at preconception (443.608\u0026ndash;1074.897) mg/d, first trimester (629.253-1091.939) mg/d, second trimester (674.119-1205.243) mg/d, and third trimester (678. 187\u0026ndash;2493. 333) mg/d, calcium may serve as a protective factor against PTB.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eAssociations of maternal dietary Calcium intake with the risk of PTB\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"12\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" morerows=\"1\" nameend=\"c2\" namest=\"c1\" rowspan=\"2\"\u003e\u003cp\u003eDietary calcium intake(mg/d)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eTerm\u003c/p\u003e\u003cp\u003e(8017)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003ePreterm\u003c/p\u003e\u003cp\u003e(\u0026lt;\u0026thinsp;37weeks)\u003c/p\u003e\u003cp\u003ecases(880)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eOR\u003csub\u003ea\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eOR\u003csub\u003ec\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;32weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e32\u0026thinsp;\u0026le;\u0026thinsp;weeks\u0026thinsp;\u0026lt;\u0026thinsp;34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e34\u0026thinsp;\u0026le;\u0026thinsp;weeks\u0026thinsp;\u0026lt;\u0026thinsp;37\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003en\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eOR\u003csub\u003ec\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003en\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003eOR\u003csub\u003ec\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003en\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003eOR\u003csub\u003ec\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003ePreconception\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026ge;359.2753\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5171\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e438\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e84\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e280\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;359.2753\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2846\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e442\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.834(1.594\u0026ndash;2.109)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.305(1.088\u0026ndash;1.564)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e88\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.209(0.811\u0026ndash;1.803)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e86\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.046(0.706\u0026ndash;1.551)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e268\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.390(1.113\u0026ndash;1.736)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePer interquartile increase\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.306(1.225\u0026ndash;1.393)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.149(1.047\u0026ndash;1.261)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.143(0.928\u0026ndash;1.408)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.087(0.890\u0026ndash;1.328)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.154(1.029\u0026ndash;1.294)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e for trend\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.0035\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.2094\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.4146\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.0145\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eFirst trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026ge;529.9334\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5209\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e427\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e79\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e279\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;529.9334\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2808\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e453\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.968(1.711\u0026ndash;2.264)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.385(1.155\u0026ndash;1.660)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.481(0.995\u0026ndash;2.205)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e91\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.354(0.920\u0026ndash;1.992)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e269\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.370(1.095\u0026ndash;1.713)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePer interquartile increase\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.337(1.253\u0026ndash;1.425)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.123(1.028\u0026ndash;1.227)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.248(1.022\u0026ndash;1.524)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.207(0.996\u0026ndash;1.463)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.069(0.959\u0026ndash;1.191)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e for trend\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.0101\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.0295\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.0545\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.2271\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eSecond trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026ge;550.5764\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5204\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e422\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e283\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;550.5764\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2813\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e458\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.088(1.746\u0026ndash;2.309)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.415(1.181\u0026ndash;1.696)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.590(1.069\u0026ndash;2.365)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.842(1.250\u0026ndash;2.716)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e265\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.276(1.021\u0026ndash;1.595)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePer interquartile increase\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.363(1.278\u0026ndash;1.454)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.176(1.082\u0026ndash;1.279)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.208(0.987\u0026ndash;1.479)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.160(0.953\u0026ndash;1.412)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.144(1.025\u0026ndash;1.278)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e for trend\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.0669\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.1393\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.0169\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eThird trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026ge;529.4478\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5498\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e437\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e300\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;529.4478\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2519\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e443\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.213(1.923\u0026ndash;2.456)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.503(1.249\u0026ndash;1.809)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e103\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e2.397(1.563\u0026ndash;3.675)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e92\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e2.016(1.353\u0026ndash;3.005)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e248\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.188(0.946\u0026ndash;1.492)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePer interquartile increase\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.411(1.322\u0026ndash;1.506)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.193(1.091\u0026ndash;1.306)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.457(1.178\u0026ndash;1.802)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.201(0.987\u0026ndash;1.463)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.129(1.012\u0026ndash;1.260)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e for trend\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.0001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.0005\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.0679\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.0303\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"12\" nameend=\"c12\" namest=\"c1\"\u003e\u003cp\u003eOR\u003csub\u003ea\u003c/sub\u003e univariate analyses.\u003c/p\u003e\u003cp\u003eOR\u003csub\u003ec\u003c/sub\u003e adjusted for weight gain during pregnancy,Mother's BMI, Mother's age,Gestational diabetes,total energy intake, monthly income per capita, maternal education level, smoking, maternal employ, multivitamin supplement, gestational hypertension, history of premature birth, reproductive history, dietary magnesium intake Supplement calcium.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eAssociations of maternal calcium supplements with the risk of PTB\u003c/h2\u003e\u003cp\u003eAs shown in associations of maternal calcium supplements with the risk of PTB (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), preconception, first trimester and the second trimester, the risk of PTB did not significantly increase among non-users of calcium supplements. However, in the third trimester, the risk of PTB significantly increased in non-users of calcium supplements (OR\u0026thinsp;=\u0026thinsp;1.498, 95% CI: 1.284\u0026ndash;1.747). Even after adjusting for confounding factors, the risk of PTB still increased, especially in the subgroup\u0026thinsp;\u0026lt;\u0026thinsp;32 weeks the risk of PTB in non-users of calcium supplements was even more significant (OR\u0026thinsp;=\u0026thinsp;3.065, 95% CI: 1.954\u0026ndash;4.809).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eAssociations of maternal Calcium supplements with the risk of PTB\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"12\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" morerows=\"1\" nameend=\"c2\" namest=\"c1\" rowspan=\"2\"\u003e\u003cp\u003eCalcium supplements\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eTerm\u003c/p\u003e\u003cp\u003e(8017)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003ePreterm\u003c/p\u003e\u003cp\u003e(\u0026lt;\u0026thinsp;37weeks)\u003c/p\u003e\u003cp\u003ecases(880)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eOR\u003csub\u003ea\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eOR\u003csub\u003ed\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;32weeks\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003e32\u0026thinsp;\u0026le;\u0026thinsp;weeks\u0026thinsp;\u0026lt;\u0026thinsp;34\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e\u003cp\u003e34\u0026thinsp;\u0026le;\u0026thinsp;weeks\u0026thinsp;\u0026lt;\u0026thinsp;37\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003en\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eOR\u003csub\u003ed\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003en\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003eOR\u003csub\u003ed\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003en\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003eOR\u003csub\u003ed\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003ePreconception\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eUsers\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e242\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNon useres\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7775\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e853\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.983(0.657\u0026ndash;1.473)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.942(0.617\u0026ndash;1.437)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e158\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.122(0.405\u0026ndash;3.105)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e166\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.093(0.395\u0026ndash;3.024)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e529\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.858(0.525\u0026ndash;1.403)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eFirst trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eUsers\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e356\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNon useres\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7661\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e847\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.193(0.829\u0026ndash;1.716)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.127(0.7721.646)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e158\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.650(0.598\u0026ndash;4.558)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e163\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.990(0.452\u0026ndash;2.166)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e526\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.067(0.678\u0026ndash;1.677)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSecond trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eUsers\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2421\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e297\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e58\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e58\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e181\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNon useres\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5596\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e583\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.849(0.733\u0026ndash;0.984)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.861(0.738\u0026ndash;1.005)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e104\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.769(0.551\u0026ndash;1.072)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e112\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.800(0.576\u0026ndash;1.111)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e367\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e0.881(0.729\u0026ndash;1.065)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eThird trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eUsers\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2958\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e247\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e174\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eNon useres\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5059\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e633\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.498(1.284\u0026ndash;1.747)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.310(1.116\u0026ndash;1.538)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e139\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e3.065(1.954\u0026ndash;4.809)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.177(0.836\u0026ndash;1.658)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e374\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e1.114(0.919\u0026ndash;1.350)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"12\" nameend=\"c12\" namest=\"c1\"\u003e\u003cp\u003eOR\u003csub\u003ea\u003c/sub\u003e univariate analyses.\u003c/p\u003e\u003cp\u003eOR\u003csub\u003ed\u003c/sub\u003e adjusted for weight gain during pregnancy,Mother's BMI, Mother's age,Gestational diabetes,total energy intake, monthly income per capita, maternal education level, smoking, maternal employ, multivitamin supplement, gestational hypertension, history of premature birth, reproductive history ,dietary calcium intake and dietary magnesium intake.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003eInteraction effects of maternal dietary magnesium and calcium intake on the risk of PTB\u003c/h2\u003e\u003cp\u003eAs shown in interaction effects of maternal dietary magnesium and calcium intake on the risk of PTB (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), preconception and third trimester increase the risk of PTB in the case of high magnesium and low calcium, with the risks being (OR\u0026thinsp;=\u0026thinsp;1.683, 95% CI: 1.392\u0026ndash;2.036) and (OR\u0026thinsp;=\u0026thinsp;1.855, 95% CI: 1.472\u0026ndash;2.338) respectively. After adjusting for confounding factors, The risks of preconception were (OR\u0026thinsp;=\u0026thinsp;1.307, 95% CI: 1.059\u0026ndash;1.614) and (OR\u0026thinsp;=\u0026thinsp;1.446, 95% CI: 1.116\u0026ndash;1.873) respectively, the risk of PTB is significantly increased in the case of low magnesium and low calcium (OR\u0026thinsp;=\u0026thinsp;1.255, 95% CI: 1.188\u0026ndash;1.325), and the risk remains significant after adjusting for confounding factors (OR\u0026thinsp;=\u0026thinsp;1.091, 95% CI: 1.019\u0026ndash;1.161). The risks of PTB in during pregnancy, first trimester, second trimester and third trimester are basically the same as those preconception when the magnesium and calcium levels are low. Moreover, there is a multiplicative interaction among preconception, during pregnancy, first trimester, second trimester and third trimester, and the interaction in the third trimester is the most significant (OR\u0026thinsp;=\u0026thinsp;1.691, 95% CI: 1.405\u0026ndash;2.035, P\u0026thinsp;\u0026lt;\u0026thinsp;0.01).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eInteraction effects of maternal dietary Magnesium and Calcium intake on the risk of PTB\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eMaternal dietary intake\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eterm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003epreterm\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eOR\u003csub\u003ea\u003c/sub\u003e\u003cem\u003e(95%CI)\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eOR\u003csub\u003ee\u003c/sub\u003e\u003cem\u003e(95%CI)\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003ePreconception\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh Magnesium high calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4769\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e400\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh Magnesium low calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1204\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e170\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.683(1.392\u0026ndash;2.036)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.307(1.059\u0026ndash;1.614)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow Magnesium high calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e402\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.062(0.892\u0026ndash;1.263)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.975(0.808\u0026ndash;1.178)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow Magnesium low calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1642\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e272\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.255(1.188\u0026ndash;1.325)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.091(1.019\u0026ndash;1.161)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e\u003cp\u003eMultiplicative interaction: \u003cem\u003eOR(95%CI)\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.248(1.045\u0026ndash;1.489) \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0144\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eDuring pregnancy\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh Magnesium high calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4316\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e345\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh Magnesium low calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e698\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e87\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.559(1.216\u0026ndash;1.999)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.135(0.858\u0026ndash;1.502)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow Magnesium high calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1050\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e94\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.058(0.940\u0026ndash;1.192)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.993(0.861\u0026ndash;1.145)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow Magnesium low calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1953\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e354\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.314(1.247\u0026ndash;1.385)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.181(1.087\u0026ndash;1.283)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e\u003cp\u003eMultiplicative interaction: \u003cem\u003eOR(95%CI)\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.622(1.346\u0026ndash;1.954) \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eFirst trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh Magnesium high calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4503\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e366\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh Magnesium low calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1037\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e131\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.554(1.259\u0026ndash;1.919)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.077(0.929\u0026ndash;1.491)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow Magnesium high calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e706\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e61\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.031(0.895\u0026ndash;1.187)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.925(0.789\u0026ndash;1.085)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow Magnesium low calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1771\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e322\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.308(1.240\u0026ndash;1.379)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.151(1.067\u0026ndash;1.243)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e\u003cp\u003eMultiplicative interaction: \u003cem\u003eOR(95%CI)\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.501(1.252\u0026ndash;1.801) \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eSecond trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh Magnesium high calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3512\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e274\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh Magnesium low calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e445\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.555(1.143\u0026ndash;2.116)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.141(0.811\u0026ndash;1.605)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow Magnesium high calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1692\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e148\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.059(0.954\u0026ndash;1.175)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.039(0.916\u0026ndash;1.179)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow Magnesium low calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2368\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e404\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.298(1.230\u0026ndash;1.370)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.163(1.065\u0026ndash;1.271)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e\u003cp\u003eMultiplicative interaction: \u003cem\u003eOR(95%CI)\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.525(1.269\u0026ndash;1.832) \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eThird trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh Magnesium high calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4582\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e351\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh Magnesium low calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e739\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e105\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.855(1.472\u0026ndash;2.338)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.446(1.116\u0026ndash;1.873)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow Magnesium high calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e916\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e86\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.107(0.979\u0026ndash;1.252)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.090(0.943\u0026ndash;1.259)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow Magnesium low calcium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1780\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e338\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.353(1.283\u0026ndash;1.427)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.237(1.142\u0026ndash;1.339)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e\u003cp\u003eMultiplicative interaction: \u003cem\u003eOR(95%CI)\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.691(1.405\u0026ndash;2.035) \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e\u003cp\u003eOR\u003csub\u003ea\u003c/sub\u003e univariate analyses.\u003c/p\u003e\u003cp\u003eOR\u003csub\u003ee\u003c/sub\u003e adjusted for weight gain during pregnancy, mother's BMI, total energy intake, monthly income per capita, maternal education level, smoking, maternal employ, multivitamin supplement, gestational hypertension, history of premature birth, reproductive history and dietary Magnesium intake.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eInteraction effects of maternal dietary magnesium intake, calcium supplements and dietary calcium intake on the risk of PTB\u003c/b\u003e\u003c/p\u003e\u003cp\u003eAs shown in interaction effects of maternal dietary magnesium intake、calcium supplements and dietary calcium intake on the risk of PTB (Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), in the preconception and second trimester groups, the intake of magnesium, calcium, and calcium supplements was not significantly associated with the risk of PTB. However, in the first trimester and third trimester groups, regardless of whether calcium supplements were used or not, the group with low calcium and magnesium intake had a significantly increased risk of PTB. Specifically, for the first trimester (OR\u0026thinsp;=\u0026thinsp;1.085, 95% CI: 1.011\u0026ndash;1.165), and for the third trimester (OR\u0026thinsp;=\u0026thinsp;1.106, 95% CI: 1.028\u0026ndash;1.189), and for the first trimester (OR\u0026thinsp;=\u0026thinsp;1.073, 95% CI: 1.022\u0026ndash;1.126), and for the third trimester(OR\u0026thinsp;=\u0026thinsp;1.113, 95% CI: 1.057\u0026ndash;1.172). Moreover, there was a multiplicative interaction effect in all four pregnancy periods, showed a relatively significant risk of PTB during the first trimester(OR\u0026thinsp;=\u0026thinsp;1.063, 95% CI: 1.001 \u0026minus;\u0026thinsp;1.128).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eInteraction effects of maternal dietary Magnesium intake、Calcium supplements and dietary Calcium intake on the risk of PTB\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"8\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" morerows=\"2\" nameend=\"c2\" namest=\"c1\" rowspan=\"3\"\u003e\u003cp\u003eMaternal dietary intake\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"6\" nameend=\"c8\" namest=\"c3\"\u003e\u003cp\u003eCalcium supplements\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e\u003cp\u003eUsers\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c8\" namest=\"c6\"\u003e\u003cp\u003eNonusers\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eterm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003epreterm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eOR\u003csub\u003ef\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eterm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003epreterm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eOR\u003csub\u003ef\u003c/sub\u003e(95%CI)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003ePreconception\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh calcium and high Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e157\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4612\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e387\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.158(0.810\u0026ndash;1.656)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh calcium and low Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.443(0.028\u0026ndash;7.097)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e385\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.009(0.712\u0026ndash;1.429)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow calcium and high Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.314(0.843\u0026ndash;2.047)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1185\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e166\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.072(0.947\u0026ndash;1.215)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow calcium and low Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.765(0.486\u0026ndash;1.205)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1609\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e268\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.092(0.979\u0026ndash;1.218)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"7\" nameend=\"c8\" namest=\"c2\"\u003e\u003cp\u003eMultiplicative interaction: OR(95%CI)\u0026thinsp;=\u0026thinsp;1.112(1.043\u0026ndash;1.187) P\u0026thinsp;=\u0026thinsp;0.0013\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eFirst pregnancy\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh calcium and high Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2461\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e185\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2042\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e181\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.015(0.893\u0026ndash;1.153)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh calcium and low Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e413\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.937(0.585\u0026ndash;1.501)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e293\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.930(0.778\u0026ndash;1.113)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow calcium and high Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e589\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.963(0.873\u0026ndash;1.062)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e448\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.063(1.001\u0026ndash;1.128)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow calcium and low Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e897\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e149\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.085(1.011\u0026ndash;1.165)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e874\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e173\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.073(1.022\u0026ndash;1.126)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"7\" nameend=\"c8\" namest=\"c2\"\u003e\u003cp\u003eMultiplicative interaction: OR(95%CI)\u0026thinsp;=\u0026thinsp;1.168(1.089\u0026ndash;1.254) P\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eSecond Trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh calcium and high Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1825\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e126\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1687\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e148\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.042(0.897\u0026ndash;1.210)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh calcium and low Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1053\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e87\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.070(0.712\u0026ndash;1.613)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e639\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e61\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.999(0.857\u0026ndash;1.165)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow calcium and high Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e228\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.922(0.789\u0026ndash;1.079)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e217\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.023(0.931\u0026ndash;1.123)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow calcium and low Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1254\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e190\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.064(0.973\u0026ndash;1.163)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1114\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e214\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.061(0.999\u0026ndash;1.127)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"7\" nameend=\"c8\" namest=\"c2\"\u003e\u003cp\u003eMultiplicative interaction: OR(95%CI)\u0026thinsp;=\u0026thinsp;1.133(1.047\u0026ndash;1.225) P\u0026thinsp;=\u0026thinsp;0.0019\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003eThird Trimester\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh calcium and high Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2510\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e179\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e2072\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e172\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.020(0.896\u0026ndash;1.161)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHigh calcium and low Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e546\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.199(0.781\u0026ndash;1.841)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e370\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.107(0.864\u0026ndash;1.197)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow calcium and high Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e390\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.013(0.906\u0026ndash;1.132)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e349\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e61\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.065(0.995\u0026ndash;1.139)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLow calcium and low Magnesium\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e914\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e153\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.106(1.028\u0026ndash;1.189)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e866\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e185\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1.113(1.057\u0026ndash;1.172)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"7\" nameend=\"c8\" namest=\"c2\"\u003e\u003cp\u003eMultiplicative interaction: OR(95%CI)\u0026thinsp;=\u0026thinsp;1.287(1.192\u0026ndash;1.389) P\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"8\" nameend=\"c8\" namest=\"c1\"\u003e\u003cp\u003eOR\u003csub\u003ef\u003c/sub\u003e adjusted for weight gain during pregnancy,Mother\u0026apos;s BMI, Mother\u0026apos;s age,Gestational diabetes,total energy intake, monthly income per capita, maternal education level, smoking, maternal employ, multivitamin supplement, gestational hypertension, history of premature birth, reproductive history.\u0026nbsp;\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this nested cohort study, we observed a significantly increased risk of preterm labor in women with low dietary calcium intake before and during pregnancy, demonstrating a dose - response relationship, The data similarly demonstrate that insufficient magnesium intake during both the second and third trimesters is associated with an elevated risk of PTB, while inadequate calcium supplements in third trimester further compounds this risk. And there is a multiplicative interaction among the three. This is the first comprehensive study to investigate the effects of dietary magnesium, calcium, and calcium supplements intakes on PTB from preconception to the entire pregnancy. Before conducting another study, the research on the relationship between dietary magnesium and calcium during the perinatal period and calcium supplements intake, as well as PTB, is still limited. There are many factors influencing premature birth, among which the influence of uterine contractions on premature birth has received extensive attention. The uterine muscle layer is composed of smooth muscle tissue, and smooth muscle tissue undergoes various physiological changes, such as hypertrophy, hyperplasia, contraction and cell apoptosis, which are very important for uterine activity. Calcium is a key regulatory factor in the contraction mechanism of smooth muscle tissue, and there are many well-defined and clinically used agonists and antagonists of uterine smooth muscle pathways, such as Ca2\u0026thinsp;+\u0026thinsp;channel blockers\u003csup\u003e[\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e. β-adrenergic receptor agonists (\u0026szlig;-agonists) bind to β-adrenergic receptors. The β-adrenergic receptors are coupled to G proteins, which activate adenylate cyclase, converting triphosphate adenosine into cAMP. An increase in cAMP activates PKA, which phosphorylates L-type calcium channels, thereby leading to an increase in calcium entering the cells. The transmembrane calcium flux is an important regulator of intracellular calcium, initiating a series of events, including the interaction of myosin light chain kinase-regulated contractile proteins (myosin and actin), ultimately resulting in muscle contraction\u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e Magnesium is an essential element for the normal functioning of the body. It participates in many metabolic pathways within cells and acts as a stabilizer for cell membranes, reducing their permeability. Magnesium is responsible for facilitating the transport of electrolytes across cell membranes to maintain homeostasis within the body. Magnesium can stabilize DNA molecules and also maintain tRNA, which is involved in normal muscle contraction, neuronal excitation, and the release of neurotransmitters\u003csup\u003e[\u003cspan additionalcitationids=\"CR27\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e. Magnesium has a relaxing effect on smooth muscles, so it is used as an inhibitor of uterine contractions in premature births, and it acts as a calcium antagonist. At the physiological level, uterine contractions are inhibited by extracellular Mg\u003csup\u003e2+\u003c/sup\u003e, and it is reported that Mg\u003csup\u003e2+\u003c/sup\u003e inhibits spontaneous depolarization. Therefore, Mg\u003csup\u003e2+\u003c/sup\u003e is used for treating uterine contractions in premature births\u003csup\u003e[\u003cspan additionalcitationids=\"CR30 CR31\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e. Another important element in maintaining the myometrial relaxation is a correct balance between ROS and NO productions. Indeed, when ROS production exceeds the myometrial antioxidant scavenging capacity, oxidative stress may increase due to consequent cellular dysfunction and tissue damage. Recently, there has also been a great deal of interest in the relaxing effect of NO on the uterine muscle layer. Therefore, NO relaxes the uterine muscle layer by increasing Mg and inhibiting Ca\u003csup\u003e2+\u003c/sup\u003e. Research reports on the mechanism of magnesium in inhibiting the contraction of the uterine muscle layer state that it rapidly induces dose-dependent inhibition of Ca\u003csup\u003e2+\u003c/sup\u003e uptake. The researchers concluded that this inhibition of calcium uptake is the reason for magnesium's inhibitory effect on spontaneous uterine muscle layer contractions\u003csup\u003e[\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e. Magnesium is crucial for bone development, stimulating the activity of phosphatases and osteoblasts, which are enzymes involved in bone formation. Magnesium deficiency directly affects bone density. Animal studies have shown that a low calcium intake can lead to osteoporosis. Animals deficient in magnesium have slender and fragile bones with severe degradation of mechanical strength. Magnesium deficiency affects the skeleton by influencing the main regulatory factors of calcium homeostasis - PTH and 1, 25(OH)2 D3\u003csup\u003e[\u003cspan additionalcitationids=\"CR37 CR38\" citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e. Most studies suggest that adequate magnesium intake during pregnancy can reduce the risk of PTB. A review article from the United States found that the results of 11 observational studies all indicated a negative correlation between serum magnesium levels and the incidence of PTB\u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. In the review titled \"Study Based on the Alliance Between Serum magnesium Levels and Preterm Labor\", Deeksha HS conducted a case-control study to determine the relationship between magnesium levels and preterm labor. The case-control study concluded that the magnesium levels of pregnant women with preterm labor were lower than those of women with full-term pregnancies\u003csup\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/sup\u003e. In a study, the results indirectly indicated that magnesium has a significant impact on the duration of pregnancy for pregnant women\u003csup\u003e[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/sup\u003e. During pregnancy, the demand for magnesium by pregnant women increases. However, most pregnant women cannot meet this increased demand. Magnesium intake during pregnancy has an impact on both the mother and the newborn's health, including fetal growth restriction and PTB\u003csup\u003e[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]\u003c/sup\u003e. Dietary habits may lead to deficiencies (including calcium) and have negative impacts on the health of mothers and their fetuses/newborns\u003csup\u003e[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/sup\u003e. Calcium intake during the third trimester of pregnancy is of vital importance for fetal skeletal development. The recommended dietary intake of calcium for pregnant women is 1000 mg per day\u003csup\u003e[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/sup\u003e. Some studies also suggest that pregnant women should consume 1.5 g \u0026minus;\u0026thinsp;2 g of calcium daily before giving birth\u003csup\u003e[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]\u003c/sup\u003e. In this study, it was found that a calcium intake lower than 359 mg per day would increase the risk of PTB. Calcium supplements during pregnancy can reduce the risk of PTB and preeclampsia in pregnant women with low dietary calcium intake\u003csup\u003e[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]\u003c/sup\u003e. Calcium supplements can prevent the occurrence of PTB. The average risk of PTB in the calcium supplements group was reduced (11 trials, 15275 women; RR\u0026thinsp;=\u0026thinsp;0.76, 95%CI 0.60 to 0.97; I\u0026sup2;=60%; low-quality evidence)\u003csup\u003e[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]\u003c/sup\u003e. A study from China indicates that the supplementation of trace elements by pregnant women in the northwest region of China is lower than that recommended by Chinese guidelines and also lower than the standards recommended by WHO\u003csup\u003e[\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]\u003c/sup\u003e. In this study, the number of pregnant women taking calcium supplements during pregnancy was relatively small. In the perspective of pregnant women, it is necessary to take folic acid and iron supplements during pregnancy. However, few people think that magnesium and calcium supplements should also be taken. In the future, pregnant women should be encouraged to pay attention to dietary consultation during pregnancy and to take necessary vitamins and trace elements supplements, so as to reduce the risk of PTB and other adverse pregnancy outcomes. In our research, we strictly ensured the quality throughout the entire process from questionnaire design to data entry and data calculation, in order to reduce recall bias and guarantee the accuracy of the calculation results. However, there are still several limitations that need to be acknowledged. Firstly, we cannot quantitatively analyze the interactions among various vitamins and trace elements in the diet. There might be potential confounding factors, although we have included the common confounding factors. Secondly, we cannot determine the calcium supplements intake. But, according to our research, pregnant women can use the dietary magnesium intake of first trimester(359.193\u0026ndash;583.690) mg/d, second trimester(369.733\u0026ndash;603.250) mg/d, third trimester(365.228-908.135) mg/d and the dietary calcium intake of preconception(443.608-1074.897) mg/d, first trimester(629.253-1091.939) mg/d, second trimester(674.119-1205.243) mg/d, third trimester(678. 187\u0026ndash;2493. 333) mg/d to prevent the occurrence of PTB risk.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eOur research indicates that, firstly, low dietary magnesium intake during the third trimester of pregnancy will increase the risk of PTB, and the absence of calcium supplements during the third trimester will also increase the risk of PTB. Secondly, insufficient dietary calcium intake before and after pregnancy will both increase the risk of PTB. Our research also found that there is a synergistic effect between magnesium and calcium intake on the risk of PTB (preconception, during pregnancy, first trimester, second trimester, and third trimester), and there is also a synergistic effect between magnesium, calcium and calcium supplements on the risk of PTB (preconception and third trimester). These results suggest that moderate increases in magnesium, calcium and calcium supplement intake before and during pregnancy are important for reducing the incidence of PTB in Lanzhou, Gansu Province, In the future, studies should be conducted on maternal biomarkers, minerals, macroelements, other trace elements and genetic data to confirm these findings and explain the underlying mechanisms.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003e\u003cstrong\u003ePTB:\u0026nbsp;\u003c/strong\u003ePreterm birth\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOR:\u003c/strong\u003e Odds ratio\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e95% CI:\u0026nbsp;\u003c/strong\u003e95% confidence interval\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRCS:\u003c/strong\u003e Multivariate-adjusted restricted cubic spline\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFFQ:\u003c/strong\u003e Semi-quantitative food frequency questionnaire\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRNI:\u003c/strong\u003e Recommended nutrient intake\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNon-PTB:\u0026nbsp;\u003c/strong\u003edelivery at or beyond 37 weeks of gestation (full-term delivery)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBMI:\u0026nbsp;\u003c/strong\u003eBody mass index\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analyzed during the current study are not made public as they contain private information of the women. However, they can be obtained from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFundings\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported in part by The Science and Technology Department Grant of Lanzhou City (No.2022-5-85), and Gansu Provincial Health Commission Research Project (No.GSWSKY2024-14; GSWSKY2024-49), and the Traditional Chinese Medicine Management Project of Gansu Province (No.GZKG-2024-43).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eZifu Wang\u003csup\u003e\u0026sup1;\u003c/sup\u003e\u003csup\u003e,\u0026sup2;\u0026dagger;\u003c/sup\u003e,\u0026nbsp;Lei Cao\u003csup\u003e\u0026sup2;\u003c/sup\u003e\u003csup\u003e,\u0026sup3;\u0026dagger;\u003c/sup\u003e,\u0026nbsp;Yuqing Li\u003csup\u003e\u0026sup2;\u003c/sup\u003e\u003csup\u003e,\u0026sup3;\u003c/sup\u003e,\u0026nbsp;Chenyan Yang\u003csup\u003e\u0026sup2;\u003c/sup\u003e\u003csup\u003e,\u0026sup3;\u003c/sup\u003e,\u0026nbsp;Baohong Mao\u003csup\u003e\u0026sup3;\u003c/sup\u003e\u003csup\u003e,\u0026sup2;\u003c/sup\u003e,\u0026nbsp;Liping Yang\u003csup\u003e\u0026sup1;\u003c/sup\u003e\u003csup\u003e,\u0026sup2;\u003c/sup\u003e,\u0026nbsp;Yue Fang\u003csup\u003e⁴\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026sup1;\u003c/sup\u003eDepartment of Public Health and Infection Management, Gansu Provincial Hospital of Traditional Chinese Medicine, Lanzhou 730000, Gansu Province, China.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026sup2;\u003c/sup\u003eSchool of Public Health, Gansu University of Chinese Medicine, Lanzhou 730000, Gansu Province, China.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026sup3;\u003c/sup\u003eDepartment of Medical Education, Gansu Provincial Maternity and Child-care Hospital (Gansu Provincial Central Hospital), Lanzhou 730050, Gansu Province, China.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e⁴\u003c/sup\u003eDepartment of Planning and Development, Gansu Provincial Hospital of Traditional Chinese Medicine, Lanzhou 730000, Gansu Province, China.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026dagger;\u003c/sup\u003e:These authors contributed equally to this work.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCorresponding Author:\u003c/p\u003e\n\u003cp\u003eBaohong Mao\u003ca href=\"mailto:[email protected],\"\u003e,\u003c/a\u003e Liping Yang, Yue Fang\u003c/p\u003e\n\u003cp\u003eLanzhou 730050, Gansu Province, China. Lanzhou 730000, Gansu Province, China.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEmail address: [email protected]\u003c/p\u003e\n\u003cp\[email protected]\u003c/p\u003e\n\u003cp\[email protected]\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eInformed consent was obtained from study participants. This research approved by Medical Ethics Committee of Gansu Provincial Maternity and Child-care Hospital [2018] The Ethics Committee of Gansu Provincial Maternity and Child-care Hospital No.(29).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the participants in the study have fully understood the research content, potential risks and benefits, and have voluntarily agreed to take part in the study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eOhuma EO, Moller AB, Bradley E, Chakwera S, Hussain-Alkhateeb L, Lewin A, Okwaraji YB, Mahanani WR, Johansson EW, Lavin T, Fernandez DE, Dom\u0026iacute;nguez GG, de Costa A, Cresswell JA, Krasevec J, Lawn JE, Blencowe H, Requejo J, Moran AC. 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PMID: 33319331; PMCID: PMC8360883.\u003c/li\u003e\n\u003cli\u003eMilman N, Paszkowski T, Cetin I, Castelo-Branco C. Supplementation during pregnancy: beliefs and science. Gynecol Endocrinol. 2016;32(7):509-516. doi:10. 3109/09513590. 2016. 1149161\u003c/li\u003e\n\u003cli\u003eParisi F, di Bartolo I, Savasi VM, Cetin I. Micronutrient supplementation in pregnancy: Who, what and how much?. Obstet Med. 2019;12(1):5-13. doi:10. 1177/1753495X18769213\u003c/li\u003e\n\u003cli\u003eSairoz, Prabhu K, Dastidar RG, Aroor AR, Rao M, Shetty S, Poojari VG, Bs V. Micronutrients in Adverse Pregnancy Outcomes. F1000Res. 2024 Jun 21;11:1369. doi: 10. 12688/f1000research. 124960. 3. PMID: 38807919; PMCID: PMC11131564. \u003c/li\u003e\n\u003cli\u003eWojcieszek AM, Bonet M, Portela A, Althabe F, Bahl R, Chowdhary N, Dua T, Edmond K, Gupta S, Rogers LM, Souza JP, Oladapo OT. WHO recommendations on maternal and newborn care for a positive postnatal experience: strengthening the maternal and newborn care continuum. BMJ Glob Health. 2023 Jan;8(Suppl 2):e010992. doi: 10.1136/bmjgh-2022-010992. PMID: 36717156; PMCID: PMC9887708.\u003c/li\u003e\n\u003cli\u003eAtallah AN, Hofmeyr GJ, Duley L. calcium supplements during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database Syst Rev. 2002;(1):CD001059. doi:10. 1002/14651858. CD001059 \u003c/li\u003e\n\u003cli\u003eHofmeyr GJ, Lawrie TA, Atallah \u0026Aacute;N, Torloni MR. calcium supplements during pregnancy for preventing hypertensive disorders and related problems. Cochrane Database Syst Rev. 2018 Oct 1;10(10):CD001059. doi: 10. 1002/14651858. CD001059. pub5. PMID: 30277579; PMCID: PMC6517256. \u003c/li\u003e\n\u003cli\u003eLiu D, Cheng Y, Dang S, Wang D, Zhao Y, Li C, Li S, Lei F, Qu P, Mi B, Zhang R, Li J, Zeng L, Yan H. Maternal adherence to micronutrient supplementation before and during pregnancy in Northwest China: a large-scale population-based cross-sectional survey. BMJ Open. 2019 Aug 8;9(8):e028843. doi: 10. 1136/bmjopen-2018-028843. PMID: 31399455; PMCID: PMC6701669. \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-pregnancy-and-childbirth","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prch","sideBox":"Learn more about [BMC Pregnancy and Childbirth](http://bmcpregnancychildbirth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/prch/default.aspx","title":"BMC Pregnancy and Childbirth","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Magnesium, Calcium, Calcium supplements, Intake levels, PTB, Nested case-control study","lastPublishedDoi":"10.21203/rs.3.rs-7305270/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7305270/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e\u003cp\u003eTo explore the association between magnesium (dietary), calcium (dietary), and calcium supplements intake levels before and during pregnancy and the risk of Preterm birth (PTB).\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eThe study subjects were pregnant women who registered at the Perinatal Medicine Center of Gansu Provincial Maternal and Child Health Hospital between March 2018 and March 2019 and whose birth outcomes could be followed up. After obtaining informed consent and ethical approval, a one-on-one dietary nutrition survey was conducted during pregnancy. A database was established based on overall dietary intake levels for statistical analysis. PTB was used as the outcome variable, and intake levels of different substances during pregnancy were used as independent variables. Unconditional logistic regression model was used to calculate the odds ratio (OR) and its 95% confidence interval (95% CI), in order to analyze the impact of different levels of substance intake on PTB. Multivariate-adjusted restricted cubic spline (RCS) models explored the nonlinear association between dietary magnesium/calcium intake and PTB risk.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eA total of 8897 pregnant women were included in the study, with 880 in the case group and 8017 in the control group. Multivariate logistic regression analysis revealed that low magnesium intake in third trimester and inadequate calcium supplements intake elevate the risk of PTB. Similarly, low calcium intake before and during pregnancy also increases this risk. Moreover, magnesium, calcium, and calcium supplements exert a synergistic effect on the risk of PTB.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eDuring the third trimester, intake of magnesium and calcium supplements should be increased. Additionally, to prevent PTB, calcium intake should be enhanced preconception and during pregnancy.\u003c/p\u003e","manuscriptTitle":"Maternal Intake of Magnesium, Calcium, and Calcium Supplements: Association with Preterm Birth Risk in a Nested Case-Control Study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-21 10:20:55","doi":"10.21203/rs.3.rs-7305270/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"206277768096484807835635369715565382264","date":"2025-08-18T01:06:29+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"269300707765065834013969035531365014286","date":"2025-08-16T13:18:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"142230395970826410281857724271621719236","date":"2025-08-15T07:52:25+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"41627247538583537589403518911504349870","date":"2025-08-13T05:46:30+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-12T23:42:23+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-12T23:38:07+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-08-11T10:48:02+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-08T02:22:41+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Pregnancy and Childbirth","date":"2025-08-08T02:15:25+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-pregnancy-and-childbirth","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prch","sideBox":"Learn more about [BMC Pregnancy and Childbirth](http://bmcpregnancychildbirth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/prch/default.aspx","title":"BMC Pregnancy and Childbirth","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8d4258bb-6942-43f2-9d03-53f9112bccd5","owner":[],"postedDate":"August 21st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-08-21T10:20:55+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-21 10:20:55","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7305270","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7305270","identity":"rs-7305270","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}