First Establishment of Trimester- and Season-Specific Serum 25(OH)D Reference Intervals in Shaanxi Pregnant Women: Addressing General Population Standard Limitations for Precise Perinatal Vitamin D Supplementation

First Establishment of Trimester- and Season-Specific Serum 25(OH)D Reference Intervals in Shaanxi Pregnant Women: Addressing General Population Standard Limitations for Precise Perinatal Vitamin D Supplementation | 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 First Establishment of Trimester- and Season-Specific Serum 25(OH)D Reference Intervals in Shaanxi Pregnant Women: Addressing General Population Standard Limitations for Precise Perinatal Vitamin D Supplementation Yanqin Liu, Yitong Lu, Jian Yuan, Guibin Bai, Xuan Zhang, Xinwen Zhang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9067533/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Background Current clinical practice relies on general population reference intervals (RIs) for serum 25-hydroxyvitamin D (25(OH)D), which fail to account for pregnancy-specific physiological changes and seasonal fluctuations—leading to misclassification of deficiency/insufficiency and inappropriate supplementation. This study aimed to for the first time establish trimester- and season-specific 25(OH)D RIs for pregnant women in Shaanxi, China, to resolve the inaccuracy of pregnancy population standards and guide precision supplementation. Methods A retrospective analysis was conducted on 33,612 women of childbearing age (7,477 pre-pregnant, 26,135 pregnant) who underwent 25(OH)D testing at Xi'an People's Hospital (Xi'an Fourth Hospital) (January 2018–October 2020). Participants were stratified by gestational trimester and blood collection season. Serum 25(OH)D was measured via enzyme-linked immunosorbent assay (ELISA; EUROIMMUN, EI2600-9601G; inter-assay CV ≤ 8%). Due to right-skewed distribution, 95% RIs were defined as the 2.5th–97.5th percentiles, with non-parametric tests (Kruskal-Wallis/Mann-Whitney U) for group comparisons. ‌ Results Serum 25(OH)D levels were right-skewed (P < 0.05). Pre-pregnant levels (35.29 ± 14.49 nmol/L) were higher than the first trimester (32.12 ± 10.38 nmol/L, P < 0.001), with a gradual increase across gestation (third trimester: 41.58 ± 15.04 nmol/L, P < 0.01). Seasonal variations were pronounced (summer: 41.28 ± 14.07 nmol/L; winter: 34.35 ± 12.45 nmol/L, P < 0.01). The highest deficiency rate (67.63%) occurred in the first trimester during winter. The overall 95% RI for pregnant women was 20.02–80.08 nmol/L, with trimester- and season-specific RIs showing elevated limits with advancing pregnancy and higher values in summer. Conclusions Serum 25(OH)D levels in Shannxi pregnant women are influenced by gestation and season. The first establishment of trimester- and season-specific RIs overcomes the inaccuracy of general population standards, providing a scientific basis for precise 25(OH)D assessment and targeted interventions—particularly for women in the first trimester and winter—to improve maternal-neonatal health. 25-hydroxyvitamin D Pregnancy Season Reference intervals Figures Figure 1 Figure 2 Introduction Vitamin D is an essential fat-soluble vitamin for human growth and development, which is playing a critical role in calcium-phosphorus metabolism and being implicated in the pathogenesis of diabetes mellitus, asthma, malignancies, autoimmune diseases, and cardiovascular disorders [ 1 – 4 ] . It circulates primarily in two forms, vitamin D2 and D3. Due to its longer half-life and higher concentration in the circulation, 25(OH)D is widely recognized as the most reliable biomarker for evaluating systemic vitamin D status [ 5 ] . Studies have shown that Vitamin D deficiency during pregnancy has been associated with an increased risk of maternal postpartum glucose intolerance, immune dysregulation, and fetal developmental abnormalities [ 6 – 9 ] . Conversely, excessive vitamin D supplementation can lead to adverse effects such as hypercalcemia, bone pain, cardiac arrhythmia, and damage to organs like the liver, kidneys, and lungs [ 10 – 11 ] . However, current guidelines only define vitamin D nutritional status ranges for the general population, not for pregnant women [ 1 – 2 ] . Consequently, clinicians often rely on reference standards derived from non-pregnant populations—this mismatch may lead to either under-supplementation (failing to correct deficiency) or over-supplementation (increasing adverse risks). A recent study published in Nutrients (2023) titled 《Chinese Pregnant Women’s Vitamin D Status: A Cross-Sectional Study》 explicitly emphasized that "population-specific, stratified reference intervals are urgently needed to improve the accuracy of vitamin D assessment in Chinese pregnant women", which further supports the necessity and timeliness of our research. Although previous studies have highlighted the high prevalence of vitamin D deficiency in pregnant women [ 12 – 14 ] , the dynamic changes in serum 25(OH)D during pregnancy and seasonal with interaction factors remain poorly understood. Metabolic demands vary across trimesters, potentially driving 25(OH)D fluctuations. This study systematically analyzed serum 25(OH)D distribution characteristics in pregnant women across trimesters and seasons, aiming to for the first time establish trimester- and season-specific RIs for Shaanxi pregnant women—laying the foundation for clinical precision interventions. Methods Study Design and Population This retrospective study included 34,045 women of childbearing age who underwent serum 25(OH)D testing at Shaanxi People's Hospital (Shannxi Fourth Hospital) (January 2018–October 2020). Exclusion criteria: (1) Missing 25(OH)D data (n = 239); (2) Age < 20 years (n = 36, immature reproductive/metabolic systems); (3) Twin pregnancy (n = 26, higher vitamin D/calcium demands); (4) Non-spontaneous conception (n = 31, potential pre-pregnancy interventions); (5) Bone metabolic diseases (n = 16, confounding calcium-phosphorus balance); (6) Current smoking (n = 57, impaired vitamin D synthesis/absorption); (7) Thyroid diseases (n = 25, disrupted vitamin D metabolism); (8) Mental disorders (n = 3, altered lifestyle/sun exposure). Final analysis included 33,612 subjects (7,477 pre-pregnant, 26,135 pregnant). Pregnant women were Shaanxi residents (≥ 1 year), singleton, and naturally conceived, stratified by trimester: first (≤ 13 weeks), second (14–27 weeks), third (≥ 28 weeks) [ 15 ] . According to the blood collection season, they are divided into spring (March 21st - June 20th), summer (June 21st - September 20th), autumn (September 21st - December 20th), and winter (December 21st - March 20th). The study was reviewed and approved by the Ethics Committee of the Xi’an People’s Hospital (Xi’an Fourth Hospital) under the number KJLL-Z-K-2025148. ‌Serological Assay Method for 25(OH)D Fasting venous blood (3 mL) was collected in each trimester, centrifuged at 3900 × g for 5 minutes, and serum stored at 4°C. Serum 25(OH)D was measured via ELISA (EUROIMMUN, EI2600-9601G; inter-assay CV ≤ 8%), with cross-reactivity for 25(OH)D₃ (95%), 25(OH)D₂ (109%), 24,25(OH)₂D₃ (91%), 1,25(OH)₂D₃ (5%), and 1,25(OH)₂D₂ (84%). Vitamin D status was defined per Chinese national guidelines: sufficient (≥ 50 nmol/L), insufficient (30-49.99 nmol/L), deficient (< 30 nmol/L) [ 16 – 17 ] . Statistical analysis SPSS 26.0 was used for analyses. Continuous data were expressed as mean ± standard deviation (SD) or median (interquartile range) per distribution type; categorical data as n (%). Normality was tested via Kolmogorov-Smirnov (K-S) test. 95% RIs were 2.5th–97.5th percentiles (right-skewed distribution). Group comparisons used non-parametric tests (Mann-Whitney U for two groups, Kruskal-Wallis for multiple groups). P < 0.05 was statistically significant. Results Baseline Characteristics of Participants Participants were aged 20–37 years (mean: 31.4 ± 4.10 years). Pregnant women: 8,404 (32.16%) first trimester (mean gestational age: 10.7 ± 2.6 weeks), 8,892 (34.02%) second trimester (21.3 ± 3.4 weeks), 8,839 (33.82%) third trimester (33.6 ± 4.2 weeks).. Distribution of Serum 25(OH)D Levels‌ K-S test confirmed right-skewed 25(OH)D distribution in pre-pregnant and pregnant groups (P < 0.05), with a significant positive correlation between trimesters (r = 0.286, P < 0.01, Fig. 1 ). Distribution Characteristics of Serum 25(OH)D Levels in Women During Pre-pregnancy Checkup and First trimester‌ Pre-pregnant 25(OH)D levels (35.29 ± 14.49 nmol/L) were significantly higher than the first trimester (32.12 ± 10.38 nmol/L, P < 0.01, Fig. 2 ). Trimester and Seasonal Distribution of 25(OH)D Among pregnant women, the overall mean serum 25(OH)D level was (37.03 ± 13.42) nmol/L. Stratification by trimester showed a significant increasing trend with advancing pregnancy: first trimester (32.12 ± 10.38 nmol/L), second trimester (37.14 ± 12.59 nmol/L), third trimester (41.58 ± 15.04 nmol/L) (P < 0.01, Table 1 ). Stratification by trimester showed a significant increasing trend with advancing pregnancy: Seasonal variations were significant (P autumn > spring > winter (34.35 ± 12.45 nmol/L) (Fig. 1 ). Trimester-specific seasonal patterns differed: First trimester: summer > spring = autumn > winter; Second trimester: summer > autumn > spring > winter; Third trimester: summer > autumn > winter > spring (Table 1 ). Table 1 Serum 25(OH)D Levels (Mean ± SD, nmol/L) in Pregnant Women by Season and Trimester Season First Trimester (n) Second Trimester (n) Third Trimester (n) P-Value Post-Hoc Comparison Spring 31.13 ± 9.60 (2139) 35.32 ± 11.78 (2364) 35.92 ± 13.73 (2420) < 0.01 1 < 2 < 3 Summer 35.81 ± 10.99 (2304) 40.92 ± 12.82 (2561) 47.78 ± 15.79 (2079) < 0.01 1 < 2 < 3 Autumn 31.57 ± 10.51 (1959) 37.33 ± 12.83 (1992) 42.72 ± 15.28 (1736) < 0.01 1 < 2 < 3 Winter 29.47 ± 9.14 (2002) 34.23 ± 11.77 (1975) 38.20 ± 13.79 (2604) < 0.01 1 < 2 < 3 P- Value (seasonal comparison) < 0.01 < 0.01 < 0.01 - d < a,c < b; d < a < c < b; a Note: 1 = First trimester, 2 = Second trimester, 3 = Third trimester; a=Spring, b=Summer, c=Autumn, d=Winter. Post-hoc tests: Kruskal-Wallis test. Trimester- and Season-Specific 95% RIs The overall 95% RI for pregnant women was 20.02–80.08 nmol/L. Both lower (2.5th) and upper (97.5th) RI limits increased with advancing gestation across all seasons, with summer RIs consistently highest (Table 2 ). Table 2 Trimester- and Season-Specific 95% Reference Intervals (2.5th–97.5th Percentiles, nmol/L) for Serum 25(OH)D in Pregnant Women‌ Season Trimester n P2.5 ~ 97.5 2.5 5 10 50 90 95 97.5 Spring (n = 6923) First 2139 20.42 21.00 22.16 28.00 45.00 50.60 56.51 Second 2364 20.80 22.05 22.95 32.30 52.45 58.18 63.97 Third 2420 21.02 22.45 24.10 35.93 59.18 65.70 71.24 Summer (n = 6944) First 2304 20.72 21.76 22.92 34.37 51.11 55.93 59.72 Second 2561 21.86 22.98 25.32 39.60 58.89 63.49 68.28 Third 2079 23.68 25.92 28.76 45.69 69.58 75.76 80.08 Autumn (n = 5687) First 1959 20.15 20.54 21.47 28.39 46.67 52.84 58.70 Second 1992 21.19 22.10 23.46 34.61 55.71 62.41 68.15 Third 1736 21.68 22.94 25.08 39.75 64.97 73.44 78.57 Winter (n = 6581) First 2002 20.56 20.92 22.07 25.88 42.48 49.57 54.94 Second 1975 20.63 21.06 22.51 30.56 52.11 57.78 61.97 Third 2604 21.05 22.59 23.83 34.92 58.14 64.93 72.05 Distribution of Serum 25(OH)D Levels in Pregnant Women‌ Overall deficiency rate: 38.59% of pregnant women were deficient (< 30 nmol/L), 44.27% were insufficient (30-49.99 nmol/L), and only 17.14% were sufficient (≥ 50 nmol/L) (Table 3 ). The deficiency rate was highest in winter (48.86%) and lowest in summer (24.49%). From a gestational perspective, the deficiency rate was most pronounced in the first trimester across all seasons, peaking at 67.63% during winter. This rate improved with advancing pregnancy, dropping to 12.17% in the summer third trimester. The normal (sufficiency) rate varied nearly 9-fold, from a low of 4.55% in the winter first trimester to a high of 41.27% in the summer third trimester. Table 3 Vitamin D Status Distribution (n, %) in Pregnant Women by Season and Trimester Season Trimester n Range (nmol/L) P-Value Deficient (< 30 nmol/L) Insufficient (30–49.99 nmol/L) Sufficient (≥ 50 nmol/L) Total - 26135 10085 (38.59) 11571 (44.27) 4479 (17.14) - Spring - 6923 2974 (42.96) 3019 (43.61) 930 (13.43) - First 2139 1230 (57.50) 795 (37.17) 114 (5.33) < 0.0001 Second 2364 995 (42.09) 1052 (44.50) 317 (13.41) Third 2420 749 (30.95) 1172 (48.43) 499 (20.62) Summer - 6944 1701 (24.49) 3501 (50.42) 1742 (25.09) - First 2304 863 (37.46) 1185 (51.43) 256 (11.11) < 0.0001 Second 2561 585 (22.84) 1348 (52.64) 628 (24.52) Third 2079 253 (12.17) 968 (46.56) 858 (41.27) Autumn - 5687 2194 (38.58) 2534 (44.56) 959 (16.86) - First 1959 1098 (56.05) 717 (36.60) 144 (7.35) < 0.0001 Second 1992 707 (35.49) 950 (47.69) 335 (16.81) Third 1736 389 (22.41) 867 (49.94) 480 (27.64) Winter - 6581 3216 (48.86) 2517 (38.25) 848 (12.89) - First 2002 1354 (67.63) 557 (27.82) 91 (4.55) < 0.0001 Second 1975 941 (47.65) 791 (40.05) 243 (12.30) Third 2604 921 (35.37) 1169 (44.89) 514 (19.74) Influencing Factors of Serum 25(OH)D Levels in Pregnant Women Standardized regression analysis showed that was a significant interaction between season and gestational trimester on 25(OH)D distribution (P < 0.0001). Summer and autumn had the strongest positive effects on 25(OH)D levels, followed by spring, with winter and gestational week having smaller effects (Tables 4 – 5 ). Table 4 Summary of Models for 25(OH)D Levels Across Different Periods Models R R 2 Adjusted R² Standard Error of Estimate Change Statistics Durbin-Watson Adj. R² Adj. F df1 df2 Sig. for F-change 1 0.262 a 0.069 0.069 11.90892 0.069 510.654 1 6922 0.000 1.514 2 0.337 b 0.113 0.113 13.24674 0.113 888.452 1 6943 0.000 1.322 3 0.328 c 0.108 0.108 12.91759 0.108 686.063 1 5686 0.000 1.347 4 0.291 d 0.085 0.085 11.91499 0.085 609.534 1 6580 0.000 1.480 5 0.287 e 0.082 0.082 12.84840 0.082 2340.167 1 26134 0.000 1.309 Note‌: Model predictors: a: spring, b: summer, c: autumn, d: winter, e: pregnancy. Dependent variable: serum 25(OH)D levels. Table 5 Regression Coefficients for 25(OH)D Levels Models Unstandardized Coefficients Standardized Coefficients t Sig. 95.0% CI of B B ‌Standard Error‌ trial version Lower Bound Upper Bound 1 constant 27.208 0.388 70.182 0.000 26.448 27.968 Spring 3.990 0.177 0.262 22.598 0.000 3.644 4.336 2 constant 29.532 0.425 69.508 0.000 28.700 30.365 Summer 5.969 0.200 0.337 29.807 0.000 5.576 6.362 3 constant 26.054 0.451 57.759 0.000 25.170 26.938 Autumn 5.577 0.213 0.328 26.193 0.000 5.159 5.994 4 constant 25.227 0.398 63.459 0.000 24.447 26.006 Winter 0.396 0.016 0.291 24.689 0.000 0.365 0.428 5 constant 27.479 0.213 129.154 0.000 27.062 27.896 Pregnancy 0.430 0.009 0.287 48.375 0.000 0.413 0.448 Note: Dependent variable: serum 25(OH)D levels. B: unstandardized coefficient; CI: confidence interval. Discussion This large-scale study for the first time establishes trimester- and season-specific 25(OH)D RIs for Shaanxi pregnant women, addressing the critical gap of applying general population standards to pregnant women. The overall mean 25(OH)D level (37.03 ± 13.42 nmol/L) falls in the insufficiency range, consistent with high vitamin D deficiency/insufficiency prevalence in Chinese pregnant women [18-19] . The impact of maternal vitamin D levels during pregnancy on both the mother and fetus remains controversial. Most studies link sufficient vitamin D levels to better maternal and fetal outcomes [4 , 20] . While, a limited number of studies suggest that vitamin D deficiency does not increase the risk of pregnancy complications [21-22] . Notably, this controversy may partly stem from the use of inappropriate reference standards—general population RIs do not account for the increased vitamin D demand in pregnancy (e.g., fetal skeletal development, placental metabolism) or seasonal variations in UVB exposure (the primary source of cutaneous vitamin D synthesis). Our stratified RIs address this issue by providing trimester- and season-specific cut-offs, enabling more accurate identification of true deficiency/insufficiency and avoiding misclassification based on irrelevant standards. Trimester and Seasonal Effects on 25(OH)D. We noted a significant rise in serum 25(OH)D levels with advancing pregnancy (first trimester: 32.12 ± 10.38 nmol/L; third trimester: 41.58 ± 15.04 nmol/L), attributed to placental maturation (augmented 1α-hydroxylase activity, converting 25(OH)D to active 1,25(OH)₂D) and improved mid-to-late pregnancy vitamin D supplementation adherence [23-24] , seasonal differences were prominent, with summer levels (41.28 ± 14.07 nmol/L) significantly higher than winter (34.35 ± 12.45 nmol/L); season is a key determinant of 25(OH)D levels [18 , 25] , particularly in Shaanxi (Northwest China): summer’s high UVB (critical for cutaneous vitamin D₃ synthesis) enhances production, whereas winter’s shorter daylight, increased haze (diminished UV exposure), and cold (reduced outdoor activity) reduce levels. Notably, season and trimester interacted significantly, with summer reference intervals (RIs) consistently higher than winter RIs across all trimesters [16 , 26-27] . Based on these findings—especially the 67.63% winter first-trimester deficiency rate (highest among subgroups)—we propose clinical/public health recommendations: 1) Priority screening: Mandate 25(OH)D testing for Shaanxi’s first-trimester (≤ 13 weeks) pregnant women, particularly winter conceptions (Dec–Mar), to early identify deficiency/insufficiency (critical for fetal organ development) and prevent delayed intervention via general population RIs; 2) Personalized supplementation dosage: Supplementation should be adjusted by season and trimester, with winter doses potentially increased compared to summer given reduced UVB exposure; 3) Lifestyle guidance: Encourage safe sun exposure and increased intake of vitamin D-rich foods, which is particularly important for women in winter or with limited outdoor activity; 4) Regular re-evaluation: Pregnant women with initial deficiency/insufficiency should have their 25(OH)D levels rechecked every 8–12 weeks, and if levels fail to reach the normal range (≥ 50 nmol/L), the supplementation dose can be adjusted incrementally to ensure adequate vitamin D status before delivery. The Distribution of Vitamin D Status Based on Serum 25(OH)D Levels Currently, pregnant women are a high-risk group for vitamin D deficiency globally [18-19 , 26-27] . Internationally, the vitamin D deficiency rate is approximately 62% among pregnant women in Indonesia [28] , 65.2% in African-American pregnant women [29] , and 74.1% in Belgium [30] . Domestically, the serum 25(OH)D deficiency rate among pregnant women is 39.16% in Changsha, while the combined rate of deficiency and insufficiency in Shenzhen is 76.7% [18 , 31] . Our study found an overall deficiency rate of 38.59% in Shannxi, which is severe, especially during the first trimester and winter months (67.63%). Interpreted via trimester-season-specific RIs, these rates gain greater clinical significance: the highest deficiency rate (67.63%) occurred in first-trimester winter (corresponding RI: 20.56-54.94 nmol/L, the lowest), marking this subgroup as most at risk of true deficiency and in urgent need of intervention. These data confirm the trimester-season-specific RIs are both scientifically valid and clinically relevant, identifying high-risk subgroups easily overlooked by general population standards. The established RIs provide a valuable tool for precise vitamin D assessment in Shaanxi and similar regions with distinct seasonal variations. Particularly for first-trimester and winter pregnant women, RIs-based vitamin D supplementation can effectively raise serum 25(OH)D levels, reducing maternal-fetal complication risks. Additionally, this study suggests that alongside supplementation, appropriate sun exposure and improved dietary structure help pregnant women achieve and maintain 25(OH)D levels within the corresponding trimester-season RIs, offering a comprehensive approach to perinatal vitamin D nutrition management. Limitations This study has several limitations that need to be acknowledged: 1) Retrospective design constraints: Data on potential confounders such as socioeconomic status, detailed lifestyle factors , occupation, and health literacy were not available. These factors may affect serum 25(OH)D levels; 2) Observational nature: The study only describes the distribution of 25(OH)D levels and their association with trimester/season, but cannot establish causal relationships between 25(OH)D levels and pregnancy outcomes, and our studies will validate RI clinical utility in future. Future prospective cohort studies should incorporate the above missing variables and validate the clinical utility of our RIs by assessing whether supplementation based on these RIs can reduce adverse pregnancy outcomes. Conclusion Serum 25(OH)D levels in Shaanxi pregnant women are influenced by gestational trimester and season, with high insufficiency prevalence. The first establishment of trimester- and season-specific RIs overcomes general population standard inaccuracies, providing a scientific basis for precise vitamin D assessment. Targeted interventions for first-trimester and winter pregnant women are essential to improve maternal-neonatal health, contributing to perinatal vitamin D precision management in Northwest China. Abbreviations 25(OH)D 25-hydroxyvitamin D ELISA enzyme-linked immunosorbent assay RIs ‌reference intervals UVB Ultraviolet B VDR Vitamin D receptor SD Standard deviation Declarations Acknowledgements We sincerely thank our laboratory colleagues for their assistance with reagent preparation and equipment maintenance. We also extend our gratitude to the funds that have rendered us assistance and suppor. Authors’ contributions YL is the Principal Investigator for this study and prepared the first draft of the manuscript, YL and GB as co-researchers contributed to data collection and manuscript revision, JY provided guidance on data analysis, XZ offered suggestions on the details of the manuscript, and XZ made significant revised the paper's framework and the final revisions.. All authors read and approved the final manuscript. Funding This work was supported by Research Key Medical Project of Shannxi Municipal Bureau of Science and Technology (24YXYJ0026), Incubation Fund of Shannxi People's Hospital (Shannxi Fourth Hospital) (No. FZ-93), Social Development Project of Shaanxi Provincial Department of Science and Technology (2025SF-YBXM-228), and Incubation Fund of Shannxi People's Hospital (Shannxi Fourth Hospital) (No. FZ-2025-102). Data availability The datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request. Ethical approval and consent to participate This retrospective study used de-identified data retrieved from the hospital's information system. According to the Ethical Guidelines for Medical Research Involving Human Subjects issued by the National Health Commission of China, this study was exempt from ethical review and did not require informed consent. Consent for publication Not applicable. Competing interests The authors declare that they have no competing interests. Author details 1 Shannxi People's Hospital (Shannxi Fourth Hospital), Shannxi 710004, Shaanxi Province, China. E-mail: [email protected] References Wen-Chien Y, Ramaa C, Karen MO, Christopher RS, Emily RS. The Effects of Vitamin D Supplementation During Pregnancy on Maternal, Neonatal, and Infant Health: A Systematic Review and Meta-analysis. NUTR REV 2025, 83(3). 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Maternal excess adiposity and serum 25-hydroxyvitamin D < 50 nmol/L are associated with elevated whole body fat mass in healthy breastfed neonates.BMC PREGNANCY CHILDB 2022, 22(1). Carla E, Amirhossein Y, Valeria G, Omar O, Mira B, Gloria S, Razan Z, Nour El Hoda E, Maya K, Diana K, James PW, Mirella AZD, Farah A, Nadeen H, Randa H, Firass A, Nicolai P. The Sunshine Paradox: Unraveling Risk Factors for Low Vitamin D Status Among Non-Pregnant Women in Lebanon. NUTRIENTS. 2025, 17(5). Buthaina Yusuf A, Afnan F, Sabika A, Simone P. Prevalence and Risk Factors for Vitamin D Deficiency in Children and Adolescents in the Kingdom of Bahrain. NUTRIENTS. 2023, 15(3). Magali R, Tom DT, Aashima D, Heba Hassan E, Giampiero IB, Kevin DC. Serum 25-hydroxyvitamin D threshold and risk of rickets in young children: a systematic review and individual participant data meta-analysis to inform the development of dietary requirements for vitamin D. EUR J NUTR 2024, 63(3). Christopher J, Clifford G, Vitamin JR. D: 100 years of discoveries, yet controversy continues. The lancet. Diabetes Endocrinol 2023, 11(5). Roger B, Leen A, Oscar Rosero O. Calcifediol (25OH Vitamin D 3 ) Deficiency: A Risk Factor from Early to Old Age. NUTRIENTS 2022, 14(6). Ankana G, Jennifer AT, Sarah F, Shiao-Y C, Melissa W, Janesh G, Mark DK, Stephane RG, Martin H. Vitamin D, the placenta and early pregnancy: effects on trophoblast function. J Endocrinol 2018, 236(2). Qian-Han X, Kahindo PM, Yu-Jing Z, Huan W, Xin-Xiu L, Ai-Hua L. Altered vitamin D metabolism is involved in the dysregulation of γδT cell function and their crosstalk with trophoblasts in recurrent pregnancy loss. American journal of reproductive immunology (New York, N.Y.: 1989) 2023, 89(6). Tarek B. Seasonal Variations in 25-Hydroxyvitamin D Levels among Pediatric Patients Attending the Healthcare Centre. NUTRIENTS. 2024, 16(3). Hye Ran S, Hyo Jeong P, SuJin S, Sun Yung L. Dietary vitamin D intake in low ultraviolet irradiation seasons is associated with a better nutritional status of vitamin D in Korean adults according to the 2013–2014 National Health and Nutrition Examination Survey. New York, N.Y.): Nutrition research; 2022. p. 105. Ying P, Shao Z, Qin L, Cai-Bo W, Wen-Hua Z, Xian-An S, Bing L, Li-Wen S, Yanjun Z. Investigating the relationship between 25-hydroxyvitamin D and thyroid function in second-trimester pregnant women. Gynecol endocrinology: official J Int Soc Gynecol Endocrinol 2018, 34(4). Sheela S, R R, K P, K N M MMM, Kalpana SS. B. Prevalence of vitamin D deficiency among South Indian pregnant women. J FAM MED PRIM CARE 2022, 11(6). Hongbing S. Recent Surge in Severe 25-hydroxyvitamin D Deficiency Among African American Children and Pregnant Women: Implications for Rickets. J RACIAL ETHN HEALTH; 2025. Abdurrahman Avar Ö, Yasemin EG, Mustafa K, Deniz YS, Yusuf E, Yakup Ç, Günal B. Vitamin D Deficiency in Pregnant Women and Their Infants. J CLIN RES PEDIATR E 2018, 10(1). Lijun Z, Rui C, Baoting N, Yuhong D, Yuxia L, Zhikang X, Caifeng M, Jikun D, Helu L. High prevalence of vitamin D deficiency in Shenzhen pregnant women. The journal of maternal-fetal & neonatal medicine: the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies. Int Soc Perinat Obstetricians 2022, 35(25). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 08 Apr, 2026 Editor assigned by journal 06 Apr, 2026 Editor invited by journal 19 Mar, 2026 Submission checks completed at journal 19 Mar, 2026 First submitted to journal 19 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-9067533","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":623885838,"identity":"6e920247-7394-45b0-9018-b8fe0bbb2970","order_by":0,"name":"Yanqin Liu","email":"","orcid":"","institution":"Shannxi People's Hospital (Shannxi Fourth Hospital)","correspondingAuthor":false,"prefix":"","firstName":"Yanqin","middleName":"","lastName":"Liu","suffix":""},{"id":623885839,"identity":"f3a81717-e157-4e2a-9e70-5fe4fc337898","order_by":1,"name":"Yitong Lu","email":"","orcid":"","institution":"Shannxi People's Hospital (Shannxi Fourth Hospital)","correspondingAuthor":false,"prefix":"","firstName":"Yitong","middleName":"","lastName":"Lu","suffix":""},{"id":623885840,"identity":"cdfba7dc-4003-4312-ab0c-87b6f0193320","order_by":2,"name":"Jian Yuan","email":"","orcid":"","institution":"Shannxi People's Hospital (Shannxi Fourth Hospital)","correspondingAuthor":false,"prefix":"","firstName":"Jian","middleName":"","lastName":"Yuan","suffix":""},{"id":623885841,"identity":"686cbc2f-dc0c-4a90-ae9d-38b81b12d8cd","order_by":3,"name":"Guibin Bai","email":"","orcid":"","institution":"Shannxi People's Hospital (Shannxi Fourth Hospital)","correspondingAuthor":false,"prefix":"","firstName":"Guibin","middleName":"","lastName":"Bai","suffix":""},{"id":623885842,"identity":"3c93d6b1-71fe-4b95-b338-7643c0269148","order_by":4,"name":"Xuan Zhang","email":"","orcid":"","institution":"Shannxi People's Hospital (Shannxi Fourth Hospital)","correspondingAuthor":false,"prefix":"","firstName":"Xuan","middleName":"","lastName":"Zhang","suffix":""},{"id":623885843,"identity":"2c0fabc1-6c04-4610-91b0-19f6592ad686","order_by":5,"name":"Xinwen Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyUlEQVRIiWNgGAWjYDACZhBhAGYdOPDhB2la2BIPzuwhzT4e48McbESoMzjO/OwxT8GdxH7png+HGXgY5PnFDuDXItnMZm44w+BZ4sw5ZzccLrBgMJw5OwG/Fn5mBjOJDwaHczfcyN1weAYPQ4LBbQJa2JjZv0kkALXsv5Hz4DAPGxFa+Jl5oLZI5DAQp0WymadMcobB4foZN9IMgIEsQdgvBuePb5Pm+XPYmH9G8uMPH37YyPNLE9CCDiRIUz4KRsEoGAWjADsAAFpJQ3hkJoWcAAAAAElFTkSuQmCC","orcid":"","institution":"Shannxi People's Hospital (Shannxi Fourth Hospital)","correspondingAuthor":true,"prefix":"","firstName":"Xinwen","middleName":"","lastName":"Zhang","suffix":""}],"badges":[],"createdAt":"2026-03-09 02:38:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9067533/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9067533/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107245474,"identity":"5d3e8722-4329-403c-a2d3-9b94c151883e","added_by":"auto","created_at":"2026-04-19 08:05:27","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":191631,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of serum 25(OH)D levels across trimesters. (A) First trimester, (B) Second trimester, (C) Third trimester. All distributions are right-skewed (K-S test, P \u0026lt; 0.05).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-9067533/v1/6e59dc11e09330c1fe854560.png"},{"id":107245475,"identity":"190a935b-ad8d-4d3a-bea0-ebae41916a69","added_by":"auto","created_at":"2026-04-19 08:05:27","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":41717,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of serum 25(OH)D levels between pre-pregnant and first-trimester women. Data are expressed as mean ± SD. P \u0026lt; 0.01 (Mann-Whitney U test).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-9067533/v1/33cbfed552c73596f164f326.png"},{"id":107484390,"identity":"dc7da790-e03e-41f7-b384-9209465d7a2a","added_by":"auto","created_at":"2026-04-22 02:31:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":908011,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9067533/v1/6ab47952-35af-4d3c-b269-5e98731632bd.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"First Establishment of Trimester- and Season-Specific Serum 25(OH)D Reference Intervals in Shaanxi Pregnant Women: Addressing General Population Standard Limitations for Precise Perinatal Vitamin D Supplementation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eVitamin D is an essential fat-soluble vitamin for human growth and development, which is playing a critical role in calcium-phosphorus metabolism and being implicated in the pathogenesis of diabetes mellitus, asthma, malignancies, autoimmune diseases, and cardiovascular disorders\u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. It circulates primarily in two forms, vitamin D2 and D3. Due to its longer half-life and higher concentration in the circulation, 25(OH)D is widely recognized as the most reliable biomarker for evaluating systemic vitamin D status\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. Studies have shown that Vitamin D deficiency during pregnancy has been associated with an increased risk of maternal postpartum glucose intolerance, immune dysregulation, and fetal developmental abnormalities\u003csup\u003e[\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. Conversely, excessive vitamin D supplementation can lead to adverse effects such as hypercalcemia, bone pain, cardiac arrhythmia, and damage to organs like the liver, kidneys, and lungs\u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e. However, current guidelines only define vitamin D nutritional status ranges for the general population, not for pregnant women\u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. Consequently, clinicians often rely on reference standards derived from non-pregnant populations\u0026mdash;this mismatch may lead to either under-supplementation (failing to correct deficiency) or over-supplementation (increasing adverse risks). A recent study published in Nutrients (2023) titled 《Chinese Pregnant Women\u0026rsquo;s Vitamin D Status: A Cross-Sectional Study》 explicitly emphasized that \"population-specific, stratified reference intervals are urgently needed to improve the accuracy of vitamin D assessment in Chinese pregnant women\", which further supports the necessity and timeliness of our research. Although previous studies have highlighted the high prevalence of vitamin D deficiency in pregnant women\u003csup\u003e[\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e, the dynamic changes in serum 25(OH)D during pregnancy and seasonal with interaction factors remain poorly understood. Metabolic demands vary across trimesters, potentially driving 25(OH)D fluctuations. This study systematically analyzed serum 25(OH)D distribution characteristics in pregnant women across trimesters and seasons, aiming to for the first time establish trimester- and season-specific RIs for Shaanxi pregnant women\u0026mdash;laying the foundation for clinical precision interventions.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy Design and Population\u003c/h2\u003e \u003cp\u003eThis retrospective study included 34,045 women of childbearing age who underwent serum 25(OH)D testing at Shaanxi People's Hospital (Shannxi Fourth Hospital) (January 2018\u0026ndash;October 2020). Exclusion criteria: (1) Missing 25(OH)D data (n\u0026thinsp;=\u0026thinsp;239); (2) Age\u0026thinsp;\u0026lt;\u0026thinsp;20 years (n\u0026thinsp;=\u0026thinsp;36, immature reproductive/metabolic systems); (3) Twin pregnancy (n\u0026thinsp;=\u0026thinsp;26, higher vitamin D/calcium demands); (4) Non-spontaneous conception (n\u0026thinsp;=\u0026thinsp;31, potential pre-pregnancy interventions); (5) Bone metabolic diseases (n\u0026thinsp;=\u0026thinsp;16, confounding calcium-phosphorus balance); (6) Current smoking (n\u0026thinsp;=\u0026thinsp;57, impaired vitamin D synthesis/absorption); (7) Thyroid diseases (n\u0026thinsp;=\u0026thinsp;25, disrupted vitamin D metabolism); (8) Mental disorders (n\u0026thinsp;=\u0026thinsp;3, altered lifestyle/sun exposure). Final analysis included 33,612 subjects (7,477 pre-pregnant, 26,135 pregnant). Pregnant women were Shaanxi residents (\u0026ge;\u0026thinsp;1 year), singleton, and naturally conceived, stratified by trimester: first (\u0026le;\u0026thinsp;13 weeks), second (14\u0026ndash;27 weeks), third (\u0026ge;\u0026thinsp;28 weeks)\u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e. According to the blood collection season, they are divided into spring (March 21st - June 20th), summer (June 21st - September 20th), autumn (September 21st - December 20th), and winter (December 21st - March 20th). The study was reviewed and approved by the Ethics Committee of the Xi\u0026rsquo;an People\u0026rsquo;s Hospital (Xi\u0026rsquo;an Fourth Hospital) under the number KJLL-Z-K-2025148.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e\u003c/h3\u003e\n\u003cdiv class=\"Heading\"\u003e\u003cb\u003e\u0026zwnj;Serological Assay Method for 25(OH)D\u003c/b\u003e\u003c/div\u003e \u003cp\u003eFasting venous blood (3 mL) was collected in each trimester, centrifuged at 3900 \u0026times; g for 5 minutes, and serum stored at 4\u0026deg;C. Serum 25(OH)D was measured via ELISA (EUROIMMUN, EI2600-9601G; inter-assay CV\u0026thinsp;\u0026le;\u0026thinsp;8%), with cross-reactivity for 25(OH)D₃ (95%), 25(OH)D₂ (109%), 24,25(OH)₂D₃ (91%), 1,25(OH)₂D₃ (5%), and 1,25(OH)₂D₂ (84%). Vitamin D status was defined per Chinese national guidelines: sufficient (\u0026ge;\u0026thinsp;50 nmol/L), insufficient (30-49.99 nmol/L), deficient (\u0026lt;\u0026thinsp;30 nmol/L)\u003csup\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eSPSS 26.0 was used for analyses. Continuous data were expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD) or median (interquartile range) per distribution type; categorical data as n (%). Normality was tested via Kolmogorov-Smirnov (K-S) test. 95% RIs were 2.5th\u0026ndash;97.5th percentiles (right-skewed distribution). Group comparisons used non-parametric tests (Mann-Whitney U for two groups, Kruskal-Wallis for multiple groups). P\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eBaseline Characteristics of Participants\u003c/h2\u003e \u003cp\u003eParticipants were aged 20\u0026ndash;37 years (mean: 31.4\u0026thinsp;\u0026plusmn;\u0026thinsp;4.10 years). Pregnant women: 8,404 (32.16%) first trimester (mean gestational age: 10.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6 weeks), 8,892 (34.02%) second trimester (21.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4 weeks), 8,839 (33.82%) third trimester (33.6\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2 weeks)..\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eDistribution of Serum 25(OH)D Levels\u0026zwnj;\u003c/h2\u003e \u003cp\u003eK-S test confirmed right-skewed 25(OH)D distribution in pre-pregnant and pregnant groups (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05), with a significant positive correlation between trimesters (r\u0026thinsp;=\u0026thinsp;0.286, P\u0026thinsp;\u0026lt;\u0026thinsp;0.01, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eDistribution Characteristics of Serum 25(OH)D Levels in Women During Pre-pregnancy Checkup and First trimester‌\u003c/h3\u003e\n\u003cp\u003ePre-pregnant 25(OH)D levels (35.29\u0026thinsp;\u0026plusmn;\u0026thinsp;14.49 nmol/L) were significantly higher than the first trimester (32.12\u0026thinsp;\u0026plusmn;\u0026thinsp;10.38 nmol/L, P\u0026thinsp;\u0026lt;\u0026thinsp;0.01, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eTrimester and Seasonal Distribution of 25(OH)D\u003c/h3\u003e\n\u003cp\u003eAmong pregnant women, the overall mean serum 25(OH)D level was (37.03\u0026thinsp;\u0026plusmn;\u0026thinsp;13.42) nmol/L. Stratification by trimester showed a significant increasing trend with advancing pregnancy: first trimester (32.12\u0026thinsp;\u0026plusmn;\u0026thinsp;10.38 nmol/L), second trimester (37.14\u0026thinsp;\u0026plusmn;\u0026thinsp;12.59 nmol/L), third trimester (41.58\u0026thinsp;\u0026plusmn;\u0026thinsp;15.04 nmol/L) (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Stratification by trimester showed a significant increasing trend with advancing pregnancy: Seasonal variations were significant (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01): summer (41.28\u0026thinsp;\u0026plusmn;\u0026thinsp;14.07 nmol/L) \u0026gt; autumn\u0026thinsp;\u0026gt;\u0026thinsp;spring\u0026thinsp;\u0026gt;\u0026thinsp;winter (34.35\u0026thinsp;\u0026plusmn;\u0026thinsp;12.45 nmol/L) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Trimester-specific seasonal patterns differed: First trimester: summer\u0026thinsp;\u0026gt;\u0026thinsp;spring\u0026thinsp;=\u0026thinsp;autumn\u0026thinsp;\u0026gt;\u0026thinsp;winter; Second trimester: summer\u0026thinsp;\u0026gt;\u0026thinsp;autumn\u0026thinsp;\u0026gt;\u0026thinsp;spring\u0026thinsp;\u0026gt;\u0026thinsp;winter; Third trimester: summer\u0026thinsp;\u0026gt;\u0026thinsp;autumn\u0026thinsp;\u0026gt;\u0026thinsp;winter\u0026thinsp;\u0026gt;\u0026thinsp;spring (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\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\u003eSerum 25(OH)D Levels (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD, nmol/L) in Pregnant Women by Season and Trimester\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\" colname=\"c1\"\u003e \u003cp\u003eSeason\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst Trimester (n)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSecond Trimester (n)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eThird Trimester (n)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eP-Value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePost-Hoc Comparison\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpring\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31.13\u0026thinsp;\u0026plusmn;\u0026thinsp;9.60 (2139)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e35.32\u0026thinsp;\u0026plusmn;\u0026thinsp;11.78 (2364)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e35.92\u0026thinsp;\u0026plusmn;\u0026thinsp;13.73 (2420)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u0026thinsp;\u0026lt;\u0026thinsp;2 \u0026lt; 3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSummer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e35.81\u0026thinsp;\u0026plusmn;\u0026thinsp;10.99 (2304)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40.92\u0026thinsp;\u0026plusmn;\u0026thinsp;12.82 (2561)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e47.78\u0026thinsp;\u0026plusmn;\u0026thinsp;15.79 (2079)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u0026thinsp;\u0026lt;\u0026thinsp;2 \u0026lt; 3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAutumn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31.57\u0026thinsp;\u0026plusmn;\u0026thinsp;10.51 (1959)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37.33\u0026thinsp;\u0026plusmn;\u0026thinsp;12.83 (1992)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e42.72\u0026thinsp;\u0026plusmn;\u0026thinsp;15.28 (1736)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u0026thinsp;\u0026lt;\u0026thinsp;2 \u0026lt; 3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWinter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29.47\u0026thinsp;\u0026plusmn;\u0026thinsp;9.14 (2002)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e34.23\u0026thinsp;\u0026plusmn;\u0026thinsp;11.77 (1975)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e38.20\u0026thinsp;\u0026plusmn;\u0026thinsp;13.79 (2604)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u0026thinsp;\u0026lt;\u0026thinsp;2 \u0026lt; 3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP- Value\u003c/p\u003e \u003cp\u003e(seasonal comparison)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ed\u0026thinsp;\u0026lt;\u0026thinsp;a,c\u0026thinsp;\u0026lt;\u0026thinsp;b; d\u0026thinsp;\u0026lt;\u0026thinsp;a \u0026lt; c\u0026thinsp;\u0026lt;\u0026thinsp;b; a\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003e\u003cem\u003eNote: 1\u0026thinsp;=\u0026thinsp;First trimester, 2\u0026thinsp;=\u0026thinsp;Second trimester, 3\u0026thinsp;=\u0026thinsp;Third trimester; a=Spring, b=Summer, c=Autumn, d=Winter. Post-hoc tests: Kruskal-Wallis test.\u003c/em\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eTrimester- and Season-Specific 95% RIs\u003c/h2\u003e \u003cp\u003eThe overall 95% RI for pregnant women was 20.02\u0026ndash;80.08 nmol/L. Both lower (2.5th) and upper (97.5th) RI limits increased with advancing gestation across all seasons, with summer RIs consistently highest (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\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\u003eTrimester- and Season-Specific 95% Reference Intervals (2.5th\u0026ndash;97.5th Percentiles, nmol/L) for Serum 25(OH)D in Pregnant Women\u0026zwnj;\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\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 \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSeason\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTrimester\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"7\" nameend=\"c10\" namest=\"c4\"\u003e \u003cp\u003eP2.5\u0026thinsp;~\u0026thinsp;97.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e97.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSpring (n\u0026thinsp;=\u0026thinsp;6923)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2139\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e21.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e22.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e28.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e45.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e50.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e56.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSecond\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2364\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e22.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e32.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e52.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e58.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e63.97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThird\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2420\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e21.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e24.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e35.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e59.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e65.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e71.24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eSummer (n\u0026thinsp;=\u0026thinsp;6944)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2304\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e21.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e22.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e34.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e51.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e55.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e59.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSecond\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2561\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e21.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e25.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e39.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e58.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e63.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e68.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThird\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2079\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e23.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e28.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e45.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e69.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e75.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e80.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eAutumn (n\u0026thinsp;=\u0026thinsp;5687)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1959\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e21.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e28.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e46.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e52.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e58.70\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSecond\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1992\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e21.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e34.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e55.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e62.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e68.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThird\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1736\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e21.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e25.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e39.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e64.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e73.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e78.57\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eWinter (n\u0026thinsp;=\u0026thinsp;6581)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e22.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e25.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e42.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e49.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e54.94\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSecond\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1975\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e21.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e22.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e30.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e52.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e57.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e61.97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThird\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2604\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e21.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e34.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e58.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e64.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e72.05\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\u003eDistribution of Serum 25(OH)D Levels in Pregnant Women\u0026zwnj;\u003c/h2\u003e \u003cp\u003eOverall deficiency rate: 38.59% of pregnant women were deficient (\u0026lt;\u0026thinsp;30 nmol/L), 44.27% were insufficient (30-49.99 nmol/L), and only 17.14% were sufficient (\u0026ge;\u0026thinsp;50 nmol/L) (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The deficiency rate was highest in winter (48.86%) and lowest in summer (24.49%). From a gestational perspective, the deficiency rate was most pronounced in the first trimester across all seasons, peaking at 67.63% during winter. This rate improved with advancing pregnancy, dropping to 12.17% in the summer third trimester. The normal (sufficiency) rate varied nearly 9-fold, from a low of 4.55% in the winter first trimester to a high of 41.27% in the summer third trimester.\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\u003eVitamin D Status Distribution (n, %) in Pregnant Women by Season and Trimester\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\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=\"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 \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSeason\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTrimester\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c6\" namest=\"c4\"\u003e \u003cp\u003eRange (nmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eP-Value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDeficient (\u0026lt;\u0026thinsp;30 nmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eInsufficient (30\u0026ndash;49.99 nmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSufficient (\u0026ge;\u0026thinsp;50 nmol/L)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e26135\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e10085 (38.59)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e11571 (44.27)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4479 (17.14)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpring\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6923\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2974 (42.96)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3019 (43.61)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e930 (13.43)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2139\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1230 (57.50)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e795 (37.17)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e114 (5.33)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSecond\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2364\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e995 (42.09)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1052 (44.50)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e317 (13.41)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThird\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2420\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e749 (30.95)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1172 (48.43)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e499 (20.62)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSummer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6944\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1701 (24.49)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3501 (50.42)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1742 (25.09)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2304\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e863 (37.46)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1185 (51.43)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e256 (11.11)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSecond\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2561\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e585 (22.84)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1348 (52.64)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e628 (24.52)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThird\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2079\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e253 (12.17)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e968 (46.56)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e858 (41.27)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAutumn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5687\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2194 (38.58)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2534 (44.56)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e959 (16.86)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1959\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1098 (56.05)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e717 (36.60)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e144 (7.35)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSecond\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1992\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e707 (35.49)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e950 (47.69)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e335 (16.81)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThird\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1736\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e389 (22.41)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e867 (49.94)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e480 (27.64)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eWinter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6581\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3216 (48.86)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2517 (38.25)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e848 (12.89)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFirst\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1354 (67.63)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e557 (27.82)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e91 (4.55)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.0001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSecond\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1975\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e941 (47.65)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e791 (40.05)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e243 (12.30)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThird\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2604\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e921 (35.37)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1169 (44.89)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e514 (19.74)\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\u003eInfluencing Factors of Serum 25(OH)D Levels in Pregnant Women\u003c/h2\u003e \u003cp\u003eStandardized regression analysis showed that was a significant interaction between season and gestational trimester on 25(OH)D distribution (P\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). Summer and autumn had the strongest positive effects on 25(OH)D levels, followed by spring, with winter and gestational week having smaller effects (Tables\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\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\u003eSummary of Models for 25(OH)D Levels Across Different Periods\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\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=\"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 \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eModels\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eR\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eAdjusted R\u0026sup2;\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eStandard Error of Estimate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c10\" namest=\"c6\"\u003e \u003cp\u003eChange Statistics\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eDurbin-Watson\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAdj. R\u0026sup2;\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAdj. F\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003edf1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003edf2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eSig. for F-change\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.262\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.069\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.069\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e11.90892\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.069\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e510.654\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e6922\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e1.514\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.337\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.113\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.113\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e13.24674\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.113\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e888.452\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e6943\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e1.322\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.328\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.108\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.108\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.91759\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.108\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e686.063\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e5686\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e1.347\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.291\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.085\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.085\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e11.91499\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.085\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e609.534\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e6580\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e1.480\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.287\u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.082\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.082\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e12.84840\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.082\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2340.167\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e26134\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e1.309\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"11\"\u003e\u003cem\u003eNote\u0026zwnj;: Model predictors: a: spring, b: summer, c: autumn, d: winter, e: pregnancy. Dependent variable: serum 25(OH)D levels.\u003c/em\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \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\u003eRegression Coefficients for 25(OH)D Levels\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\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=\"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 \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" morerows=\"1\" nameend=\"c2\" namest=\"c1\" rowspan=\"2\"\u003e \u003cp\u003eModels\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eUnstandardized Coefficients\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eStandardized Coefficients\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003et\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSig.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e95.0% CI of B\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eB\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026zwnj;Standard Error\u0026zwnj;\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003etrial version\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eLower Bound\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eUpper Bound\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003econstant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e27.208\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.388\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e70.182\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e26.448\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e27.968\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpring\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.990\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.177\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.262\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e22.598\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.644\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e4.336\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003econstant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e29.532\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.425\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e69.508\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e28.700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e30.365\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSummer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.969\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.337\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29.807\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e5.576\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e6.362\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003econstant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e26.054\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.451\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e57.759\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e25.170\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e26.938\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAutumn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.577\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.213\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.328\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e26.193\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e5.159\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e5.994\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003econstant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25.227\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.398\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e63.459\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e24.447\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e26.006\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWinter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.396\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.016\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.291\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e24.689\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.365\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.428\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003econstant\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e27.479\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.213\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e129.154\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e27.062\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e27.896\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePregnancy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.430\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.009\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.287\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e48.375\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.413\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.448\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003e\u003cem\u003eNote: Dependent variable: serum 25(OH)D levels. B: unstandardized coefficient; CI: confidence interval.\u003c/em\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis large-scale study for the first time establishes trimester- and season-specific 25(OH)D RIs for Shaanxi pregnant women, addressing the critical gap of applying general population standards to pregnant women. The overall mean 25(OH)D level (37.03 \u0026plusmn; 13.42 nmol/L) falls in the insufficiency range, consistent with high vitamin D deficiency/insufficiency prevalence in Chinese pregnant women\u003csup\u003e[18-19]\u003c/sup\u003e. The impact of maternal vitamin D levels during pregnancy on both the mother and fetus remains controversial. Most studies link sufficient vitamin D levels to better maternal and fetal outcomes\u003csup\u003e[4\u003c/sup\u003e, \u003csup\u003e20]\u003c/sup\u003e. While, a limited number of studies suggest that vitamin D deficiency does not increase the risk of pregnancy complications\u003csup\u003e[21-22]\u003c/sup\u003e. Notably, this controversy may partly stem from the use of inappropriate reference standards\u0026mdash;general population RIs do not account for the increased vitamin D demand in pregnancy (e.g., fetal skeletal development, placental metabolism) or seasonal variations in UVB exposure (the primary source of cutaneous vitamin D synthesis). Our stratified RIs address this issue by providing trimester- and season-specific cut-offs, enabling more accurate identification of true deficiency/insufficiency and avoiding misclassification based on irrelevant standards.\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003e\u003cstrong\u003eTrimester and Seasonal Effects on 25(OH)D.\u003c/strong\u003e\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eWe noted a significant rise in serum 25(OH)D levels with advancing pregnancy (first trimester: 32.12 \u0026plusmn; 10.38 nmol/L; third trimester: 41.58 \u0026plusmn; 15.04 nmol/L), attributed to placental maturation (augmented 1\u0026alpha;-hydroxylase activity, converting 25(OH)D to active 1,25(OH)₂D) and improved mid-to-late pregnancy vitamin D supplementation adherence\u003csup\u003e[23-24]\u003c/sup\u003e, seasonal differences were prominent, with summer levels (41.28 \u0026plusmn; 14.07 nmol/L) significantly higher than winter (34.35 \u0026plusmn; 12.45 nmol/L); season is a key determinant of 25(OH)D levels\u003csup\u003e[18\u003c/sup\u003e, \u003csup\u003e25]\u003c/sup\u003e, particularly in Shaanxi (Northwest China): summer\u0026rsquo;s high UVB (critical for cutaneous vitamin D₃ synthesis) enhances production, whereas winter\u0026rsquo;s shorter daylight, increased haze (diminished UV exposure), and cold (reduced outdoor activity) reduce levels. Notably, season and trimester interacted significantly, with summer reference intervals (RIs) consistently higher than winter RIs across all trimesters\u003csup\u003e[16\u003c/sup\u003e, \u003csup\u003e26-27]\u003c/sup\u003e. Based on these findings\u0026mdash;especially the 67.63% winter first-trimester deficiency rate (highest among subgroups)\u0026mdash;we propose clinical/public health recommendations: 1) Priority screening: Mandate 25(OH)D testing for Shaanxi\u0026rsquo;s first-trimester (\u0026le; 13 weeks) pregnant women, particularly winter conceptions (Dec\u0026ndash;Mar), to early identify deficiency/insufficiency (critical for fetal organ development) and prevent delayed intervention via general population RIs; 2) Personalized supplementation dosage: Supplementation should be adjusted by season and trimester, with winter doses potentially increased compared to summer given reduced UVB exposure; 3) Lifestyle guidance: Encourage safe sun exposure and increased intake of vitamin D-rich foods, which is particularly important for women in winter or with limited outdoor activity; 4) Regular re-evaluation: Pregnant women with initial deficiency/insufficiency should have their 25(OH)D levels rechecked every 8\u0026ndash;12 weeks, and if levels fail to reach the normal range (\u0026ge; 50 nmol/L), the supplementation dose can be adjusted incrementally to ensure adequate vitamin D status before delivery.\u003c/p\u003e\n\u003col start=\"2\"\u003e\n \u003cli\u003e\u003cstrong\u003eThe Distribution of Vitamin D Status Based on Serum 25(OH)D Levels\u003c/strong\u003e\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eCurrently, pregnant women are a high-risk group for vitamin D deficiency globally\u003csup\u003e[18-19\u003c/sup\u003e, \u003csup\u003e26-27]\u003c/sup\u003e. Internationally, the vitamin D deficiency rate is approximately 62% among pregnant women in Indonesia\u003csup\u003e[28]\u003c/sup\u003e, 65.2% in African-American pregnant women\u003csup\u003e[29]\u003c/sup\u003e, and 74.1% in Belgium\u003csup\u003e[30]\u003c/sup\u003e. Domestically, the serum 25(OH)D deficiency rate among pregnant women is 39.16% in Changsha, while the combined rate of deficiency and insufficiency in Shenzhen is 76.7%\u003csup\u003e[18\u003c/sup\u003e, \u003csup\u003e31]\u003c/sup\u003e. Our study found an overall deficiency rate of 38.59% in Shannxi, which is severe, especially during the first trimester and winter months (67.63%). Interpreted via trimester-season-specific RIs, these rates gain greater clinical significance: the highest deficiency rate (67.63%) occurred in first-trimester winter (corresponding RI: 20.56-54.94 nmol/L, the lowest), marking this subgroup as most at risk of true deficiency and in urgent need of intervention. These data confirm the trimester-season-specific RIs are both scientifically valid and clinically relevant, identifying high-risk subgroups easily overlooked by general population standards.\u003c/p\u003e\n\u003cp\u003eThe established RIs provide a valuable tool for precise vitamin D assessment in Shaanxi and similar regions with distinct seasonal variations. Particularly for first-trimester and winter pregnant women, RIs-based vitamin D supplementation can effectively raise serum 25(OH)D levels, reducing maternal-fetal complication risks. Additionally, this study suggests that alongside supplementation, appropriate sun exposure and improved dietary structure help pregnant women achieve and maintain 25(OH)D levels within the corresponding trimester-season RIs, offering a comprehensive approach to perinatal vitamin D nutrition management.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLimitations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study has several limitations that need to be acknowledged: 1) Retrospective design constraints: Data on potential confounders such as socioeconomic status, detailed lifestyle factors , occupation, and health literacy were not available. These factors may affect serum 25(OH)D levels; 2) Observational nature: The study only describes the distribution of 25(OH)D levels and their association with trimester/season, but cannot establish causal relationships between 25(OH)D levels and pregnancy outcomes, and our studies will validate RI clinical utility in future. Future prospective cohort studies should incorporate the above missing variables and validate the clinical utility of our RIs by assessing whether supplementation based on these RIs can reduce adverse pregnancy outcomes.\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eSerum 25(OH)D levels in Shaanxi pregnant women are influenced by gestational trimester and season, with high insufficiency prevalence. The first establishment of trimester- and season-specific RIs overcomes general population standard inaccuracies, providing a scientific basis for precise vitamin D assessment. Targeted interventions for first-trimester and winter pregnant women are essential to improve maternal-neonatal health, contributing to perinatal vitamin D precision management in Northwest China.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003e25(OH)D\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e25-hydroxyvitamin D\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eELISA\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eenzyme-linked immunosorbent assay\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eRIs\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e\u0026zwnj;reference intervals\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eUVB\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eUltraviolet B\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eVDR\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eVitamin D receptor\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e\u003cb\u003eSD\u003c/b\u003e\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eStandard deviation\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe sincerely thank our laboratory colleagues for their assistance with reagent preparation and equipment maintenance. We also extend our gratitude to the funds that have rendered us assistance and suppor.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYL is the Principal Investigator for this study and prepared the first draft of the manuscript, YL and GB as co-researchers contributed to data collection and manuscript revision, JY provided \u0026nbsp; guidance on data analysis, XZ offered suggestions on the details of the manuscript, and XZ made significant revised the paper\u0026apos;s framework and the final revisions.. All authors read and approved \u0026nbsp;the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by Research Key Medical Project of Shannxi Municipal Bureau of Science and Technology (24YXYJ0026), Incubation Fund of Shannxi People\u0026apos;s Hospital (Shannxi Fourth Hospital) (No. FZ-93), Social Development Project of Shaanxi Provincial Department of Science and Technology (2025SF-YBXM-228), and Incubation Fund of Shannxi People\u0026apos;s Hospital (Shannxi Fourth Hospital) (No. FZ-2025-102).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analyzed during the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis retrospective study used de-identified data retrieved from the hospital\u0026apos;s information system. According to the Ethical Guidelines for Medical Research Involving Human Subjects issued by the National Health Commission of China, this study was exempt from ethical review and did not require informed consent.\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\n\u003cp\u003e\u003cstrong\u003eAuthor details\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eShannxi People\u0026apos;s Hospital (Shannxi Fourth Hospital), Shannxi 710004, Shaanxi Province, China.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eE-mail: [email protected]\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWen-Chien Y, Ramaa C, Karen MO, Christopher RS, Emily RS. The Effects of Vitamin D Supplementation During Pregnancy on Maternal, Neonatal, and Infant Health: A Systematic Review and Meta-analysis. NUTR REV 2025, 83(3).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAndrea G, John PB, Robert AA, Giuseppe B, Daniel DB, Neil CB, Jens B, Roger B, Maria Luisa B, Felipe FC, Luigi DF, Lorenzo MD, Peter RE, Ghada El-Hajj F, Angelo F, Stefano F, Glenville J, Claudio M, Adrian RM, Salvatore M, Nicola N, Massimo P, Ren\u0026eacute; R, Anne LS, Christopher TS, Fabio Massimo U. Jyrki K V. Consensus Statement on Vitamin D Status Assessment and Supplementation: Whys, Whens, and Hows. ENDOCR REV. 2024;45(5):2222.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eK A W NCH, C DANBEB, G E-H F CECPCMD, N E L PK, O D M AM, C RR, Group SBD. IOFV. Optimisation of vitamin D status in global populations. 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NUTRIENTS 2023, 15(15).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHai-Ying C, Hong-Ping Z, Jie Y, Zhi-Qiong H, Hai-Xia X, Jiang J, Kai X, Yu T, Qian-Qian D, Jian-Qiong Z. The relationship between maternal vitamin D deficiency and glycolipid metabolism and adverse pregnancy outcome. CLIN ENDOCRINOL 2020, 93(6).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHadi G, Mohammad Rahman R. The Effect of Vitamin D3 Injection Combined With High-Intensity Interval Training on Excessive Autophagy in the Heart Tissue of Type 2 Diabetes-Induced Rats: An Analysis of the mTOR-Beclin-1-Fyco-1-Cathepsin D Pathway. CARDIOVASC THER 2025, 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXing-Qi Z, Hao-Yang W, Si-Ying H, Han-Jun Q, Bin Y, Nan J. Vitamin D Receptor Genetic Polymorphisms Associate With a Decreased Susceptibility to Extremity Osteomyelitis Partly by Inhibiting Macrophage Apoptosis Through Inhibition of Excessive ROS Production \u003cem\u003evia\u003c/em\u003e VDR-Bmi1 Signaling. FRONT PHYSIOL 2022, 13.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eErmias Sisay C, Guicheng Z, Peter LS. The serum level of vitamin D and prevalence of vitamin D deficiency among children with asthma in Asia and Africa: a systematic review and meta-analysis. Archives public health = Archives belges de sante publique 2024, 82(1).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQianqian Z, Dongjian Y, Qianwen S, Wei L, Ruoxuan L, Yanan T, Zhimin L, Baihe L, Xiya D, Meng N, Ze C, Zhenying L, Chunyu C, Dongting Y, Yi H, Xiaorui L, Jiuru Z, Hao C, Zhiwei L. Correlation of Maternal Vitamin D Status in Early Pregnancy and Vitamin D Supplementation during Pregnancy with Atopic Dermatitis in Infants: A Prospective Birth Cohort Study. NUTRIENTS. 2024, 16(13).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhaojun C, Yunxia Z, Ting W, Xia Q, Ye H, Wensheng H. The effect of maternal vitamin D deficiency during pregnancy on glycolipid metabolism of offspring rats and the improvement of vitamin D intervention after weaning. FRONT NUTR 2023, 10.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJindan P, Yan L, Zhihong M, Qi D, Jiali R, Juan W, Xiaolin H. MiR-590-3p and its targets VEGF, PIGF, and MMP9 in early, middle, and late pregnancy: their longitudinal changes and correlations with risk of fetal growth restriction. Ir J MED SCI 2022, 191(3).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKai B, Heng D, Ling L, Xuhui S, Chang L, Mujun Y, Zhihui L, Haibiao L, Peifeng K, Xianzhang H, Xinzhong W, Qiaoxuan Z, Beibei Z. Serum 25-hydroxyvitamin D status of a large Chinese population from 30 provinces by LC-MS/MS measurement for consecutive 3 years: differences by age, sex, season and province. EUR J NUTR 2023, 62(3).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMaryam R, Nathalie G, Catherine A V, Olusola F S, Shu Qin W, Dayre M, Frank R, Glenville J, Hope A W. Maternal excess adiposity and serum 25-hydroxyvitamin D \u0026lt; 50 nmol/L are associated with elevated whole body fat mass in healthy breastfed neonates.BMC PREGNANCY CHILDB 2022, 22(1).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCarla E, Amirhossein Y, Valeria G, Omar O, Mira B, Gloria S, Razan Z, Nour El Hoda E, Maya K, Diana K, James PW, Mirella AZD, Farah A, Nadeen H, Randa H, Firass A, Nicolai P. The Sunshine Paradox: Unraveling Risk Factors for Low Vitamin D Status Among Non-Pregnant Women in Lebanon. NUTRIENTS. 2025, 17(5).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eButhaina Yusuf A, Afnan F, Sabika A, Simone P. Prevalence and Risk Factors for Vitamin D Deficiency in Children and Adolescents in the Kingdom of Bahrain. NUTRIENTS. 2023, 15(3).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMagali R, Tom DT, Aashima D, Heba Hassan E, Giampiero IB, Kevin DC. Serum 25-hydroxyvitamin D threshold and risk of rickets in young children: a systematic review and individual participant data meta-analysis to inform the development of dietary requirements for vitamin D. EUR J NUTR 2024, 63(3).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChristopher J, Clifford G, Vitamin JR. D: 100 years of discoveries, yet controversy continues. The lancet. Diabetes Endocrinol 2023, 11(5).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRoger B, Leen A, Oscar Rosero O. Calcifediol (25OH Vitamin D\u003csub\u003e3\u003c/sub\u003e) Deficiency: A Risk Factor from Early to Old Age. NUTRIENTS 2022, 14(6).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnkana G, Jennifer AT, Sarah F, Shiao-Y C, Melissa W, Janesh G, Mark DK, Stephane RG, Martin H. Vitamin D, the placenta and early pregnancy: effects on trophoblast function. J Endocrinol 2018, 236(2).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQian-Han X, Kahindo PM, Yu-Jing Z, Huan W, Xin-Xiu L, Ai-Hua L. Altered vitamin D metabolism is involved in the dysregulation of γδT cell function and their crosstalk with trophoblasts in recurrent pregnancy loss. American journal of reproductive immunology (New York, N.Y.: 1989) 2023, 89(6).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTarek B. Seasonal Variations in 25-Hydroxyvitamin D Levels among Pediatric Patients Attending the Healthcare Centre. NUTRIENTS. 2024, 16(3).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHye Ran S, Hyo Jeong P, SuJin S, Sun Yung L. Dietary vitamin D intake in low ultraviolet irradiation seasons is associated with a better nutritional status of vitamin D in Korean adults according to the 2013\u0026ndash;2014 National Health and Nutrition Examination Survey. New York, N.Y.): Nutrition research; 2022. p. 105.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYing P, Shao Z, Qin L, Cai-Bo W, Wen-Hua Z, Xian-An S, Bing L, Li-Wen S, Yanjun Z. Investigating the relationship between 25-hydroxyvitamin D and thyroid function in second-trimester pregnant women. Gynecol endocrinology: official J Int Soc Gynecol Endocrinol 2018, 34(4).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSheela S, R R, K P, K N M MMM, Kalpana SS. B. Prevalence of vitamin D deficiency among South Indian pregnant women. J FAM MED PRIM CARE 2022, 11(6).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHongbing S. Recent Surge in Severe 25-hydroxyvitamin D Deficiency Among African American Children and Pregnant Women: Implications for Rickets. J RACIAL ETHN HEALTH; 2025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbdurrahman Avar \u0026Ouml;, Yasemin EG, Mustafa K, Deniz YS, Yusuf E, Yakup \u0026Ccedil;, G\u0026uuml;nal B. Vitamin D Deficiency in Pregnant Women and Their Infants. J CLIN RES PEDIATR E 2018, 10(1).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLijun Z, Rui C, Baoting N, Yuhong D, Yuxia L, Zhikang X, Caifeng M, Jikun D, Helu L. High prevalence of vitamin D deficiency in Shenzhen pregnant women. The journal of maternal-fetal \u0026amp; neonatal medicine: the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies. Int Soc Perinat Obstetricians 2022, 35(25).\u003c/span\u003e\u003c/li\u003e\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":"25-hydroxyvitamin D, Pregnancy, Season, Reference intervals","lastPublishedDoi":"10.21203/rs.3.rs-9067533/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9067533/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground \u003c/strong\u003e\u0026nbsp;Current clinical practice relies on general population reference intervals (RIs) for serum 25-hydroxyvitamin D (25(OH)D), which fail to account for pregnancy-specific physiological changes and seasonal fluctuations—leading to misclassification of deficiency/insufficiency and inappropriate supplementation. This study aimed to for the first time establish trimester- and season-specific 25(OH)D RIs for pregnant women in Shaanxi, China, to resolve the inaccuracy of pregnancy population standards and guide precision supplementation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods \u003c/strong\u003e\u0026nbsp;A retrospective analysis was conducted on 33,612 women of childbearing age (7,477 pre-pregnant, 26,135 pregnant) who underwent 25(OH)D testing at Xi'an People's Hospital \u0026nbsp;(Xi'an Fourth Hospital) (January 2018–October 2020). Participants were stratified by gestational trimester and blood collection season. Serum 25(OH)D was measured via enzyme-linked immunosorbent assay (ELISA; EUROIMMUN, EI2600-9601G; inter-assay CV ≤ 8%). Due to right-skewed distribution, 95% RIs were defined as the 2.5th–97.5th percentiles, with non-parametric tests (Kruskal-Wallis/Mann-Whitney U) for group comparisons.\u003c/p\u003e\n\u003cp\u003e‌\u003cstrong\u003eResults \u003c/strong\u003eSerum 25(OH)D levels were right-skewed (P \u0026lt; 0.05). Pre-pregnant levels (35.29 ± 14.49 nmol/L) were higher than the first trimester (32.12 ± 10.38 nmol/L, P \u0026lt; 0.001), with a gradual increase across gestation (third trimester: 41.58 ± 15.04 nmol/L, P \u0026lt; 0.01). Seasonal variations were pronounced (summer: 41.28 ± 14.07 nmol/L; winter: 34.35 ± 12.45 nmol/L, P \u0026lt; 0.01). The highest deficiency rate (67.63%) occurred in the first trimester during winter. The overall 95% RI for pregnant women was 20.02–80.08 nmol/L, with trimester- and season-specific RIs showing elevated limits with advancing pregnancy and higher values in summer.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions \u003c/strong\u003eSerum 25(OH)D levels in Shannxi pregnant women are influenced by gestation and season. The first establishment of trimester- and season-specific RIs overcomes the inaccuracy of general population standards, providing a scientific basis for precise 25(OH)D assessment and targeted interventions—particularly for women in the first trimester and winter—to improve maternal-neonatal health.\u003c/p\u003e","manuscriptTitle":"First Establishment of Trimester- and Season-Specific Serum 25(OH)D Reference Intervals in Shaanxi Pregnant Women: Addressing General Population Standard Limitations for Precise Perinatal Vitamin D Supplementation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-19 08:05:23","doi":"10.21203/rs.3.rs-9067533/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-04-08T17:23:53+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-06T11:43:53+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-03-19T19:36:45+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-19T06:51:43+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Pregnancy and Childbirth","date":"2026-03-19T06:29:31+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":"e9af8487-0c97-4d5f-8ac4-3cdef5620773","owner":[],"postedDate":"April 19th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-19T08:05:23+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-19 08:05:23","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9067533","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9067533","identity":"rs-9067533","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}