Alteration and Predictive Ability of Cervical Length for Preterm Delivery in Each Gestational Trimester

Alteration and Predictive Ability of Cervical Length for Preterm Delivery in Each Gestational Trimester | 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 Alteration and Predictive Ability of Cervical Length for Preterm Delivery in Each Gestational Trimester Qidi Zhang, Xinyue Han, Huixia Yang, Yuchun Zhu, Yumei Wei This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4005959/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background To investigate the variations in cervical length (CL) across the first, second and third trimesters and the association with preterm delivery (PTD). Methods In total, 16,352 women (32,543 measurements) who delivered singleton live births between January 1, 2020, and October 31, 2023, at Peking University First Hospitals were included in the present study. The associations between CL at three gestational weeks (9–13 + 6 , 19–23 + 6 and 29–33 + 6 weeks) and PTD were evaluated using receiver operating characteristic (ROC) curves and logistic regression analysis. The chi-square test was used for comparisons of the incidence of PTD at or below each percentile for CL with patients with CL above the 75th percentile. Results With increasing gestational age, there was a downward trend in CL at each percentile, with particularly obvious decreases in the 10th (31.5 mm and 27.1 mm), 5th (30.0 mm and 23.4 mm) and 1st (25.2 mm and 15.5 mm) percentiles after the 19th week of gestation. As gestational age increased, the predictive value of CL for PTD ≤ 34 + 6 gestational weeks and PTD < 37 gestational weeks increased. After the 19th week of gestation, CL and PTD risk were negatively correlated when CL was less than or equal to the 75th percentile (all P < 0.01). The incidence of PTD < 37 gestational weeks was significantly higher among women with CL ≤ 22.3 mm at 29–33 + 6 gestational weeks than among women with CL ≤ 25 mm. Conclusions CL progressively decreases with increasing gestational age and has emerged as a more potent predictor of PTD after the 19th week of gestation. The defining threshold of a short cervix should probably be less than 25 mm at 29–33 + 6 gestational weeks. Cervical Length Pregnancy Preterm Birth Preterm Delivery Risk Factors Ultrasonography Figures Figure 1 Figure 2 Figure 3 Introduction Complications of preterm delivery (PTD) before 37 gestational weeks are the primary cause of mortality among children under 5 years of age globally [ 1 , 2 ], as a result of respiratory disorder, feeding difficulty, impaired temperature regulation and increased risk of infection [ 3 ]. The global incidence of PTD presents an increase between 2010 and 2020, this issue continues to affect the health of children worldwide and it is crucial to reduce the incidence of PTD [ 4 ]. Cervical length (CL) ascertained by ultrasound has consistently emerged as a prominent predictor of PTD. Several previous studies have shown a significant correlation between CL during the first, second and third trimesters of pregnancy and the incidence of PTD [ 5 – 7 ]. Based on the seminal research by Lams JD et al. in 1996, the prevailing definition of a short cervix is CL < 25 mm [ 8 – 11 ]. Several studies [ 12 – 14 ] have shown that the incidence of PTD is significantly higher in pregnant women with CL < 25 mm than in those without short cervix; these studies employed CL measurements obtained from the first, second and third trimesters of pregnancy. However, importantly, the CL is a dynamic parameter that continuously changes with increasing gestational age. Previous work has shown a marked reduction in CL during the third trimester compared to the first and second trimesters [ 13 ]. Consequently, employing the cut-off value of 25 mm to delineate the short cervix across varying gestational weeks may not be entirely accurate. In the present study, we aimed to investigate the role of CL as a predictor for PTD at distinct gestational weeks by examining alterations in CL throughout different gestational periods and subsequently comparing the incidence of PTD at or below every percentile of CL within each trimester. Methods Study sample In this study, a total of 36,320 CL measurements were obtained from the medical records of 17,756 pregnant women who delivered singleton live births between January 1, 2020, and October 31, 2023, at Peking University First Hospitals in Beijing. In total, 263 pregnant women (601 measurements) were excluded because of the coexistence of PTD and uterine rupture ( n = 11), a low-lying placenta with hemorrhage ( n = 3), eclampsia ( n = 202), or placental abruption ( n = 47). And 1,141 women (3,176 measurements) were excluded due to a diagnosis of threatened preterm labor ( n = 685), shortened CL ( n = 230), or operation via cerclage ( n = 226). A total of 16,352 patients (32,543 measurements) were ultimately included in the primary analysis (Fig. 1 ): 3,768 measurements at 9–13 + 6 gestational weeks, 14,530 measurements at 19–23 + 6 gestational weeks, and 14,245 measurements at 29–33 + 6 gestational weeks. Ultrasound assessment and pregnancy outcomes Data on CL were extracted from ultrasound reports obtained during pregnancy based on measurements performed by trained obstetricians using standardized methods and criteria. The CL of all pregnant women were assessed using the single-line method [ 6 ], which measures the linear distance between the internal and external cervical os (the two endpoints of the glandular area surrounding the endocervical canal). The primary pregnancy outcome in this study was PTD, which included PTD ≤ 34 + 6 gestational weeks [ 8 ] and < 37 gestational weeks. Statistical analysis The analyses in this study were conducted with SPSS software (IBM SPSS Statistics 26.0). Based on a single-sample Kolmogorov-Smirnov test, continuous variables that were not normally distributed are presented as the median (25th-75th percentile), and categorical variables are presented as numbers and percentages. The associations between CL at various gestational weeks and PTD were evaluated using receiver operating characteristic (ROC) curves and logistic regression analysis. The chi-square test was used for comparisons of the incidence of PTD between patients at or below each percentile for CL with those with CL above the 75th percentile [ 8 ]. P < 0.05 indicated that the differences were statistically significant. Results A total of 328 (2.0%) of the 16,352 participants had PTD ≤ 34 + 6 gestational weeks, and 870 (5.3%) had PTD < 37 gestational weeks. The medians (25th-75th percentile) for maternal age, gestational age, gravidity, parity and predelivery weight were 32.0 (30.0–35.0) years, 39.3 (38.6–40.1) weeks, 1.0 (1.0–2.0), 1.0 (1.0–1.0) and 70.0 (64.0–77.0) kg, respectively. A total of 10,060 (61.5%) women gave birth by vaginal delivery, and the remaining 6,292 (38.5%) underwent cesarean section. Figure 2 shows the area under the curve (AUC) of the ROC, which indicates the predictive value of CL for PTD. As gestational age advanced, the predictive value of CL for PTD ≤ 34 + 6 gestational weeks increased, and these associations were significant after the 19th week of pregnancy (all P < 0.01). The AUC and 95% confidence interval (95% CI) at 19–23 + 6 and 29–33 + 6 gestational weeks increased gradually, with corresponding values of 0.615 (0.576–0.655) and 0.694 (0.658–0.730), respectively. Starting from the 9–13 + 6 weeks of gestation, CL demonstrated a significant predictive value for PTD < 37 gestational weeks (all P < 0.05), accompanied by a progressive increase in the AUC. The AUC (95% CI) values at 9–13 + 6 , 19–23 + 6 and 29–33 + 6 gestational weeks were 0.543 (0.502–0.584), 0.576 (0.553-0.600) and 0.632 (0.609–0.655), respectively. With increasing gestational age, a downward trend in CL was observed at each percentile, with a particularly obvious decrease at the 10th (31.5 mm and 27.1 mm), 5th (30.0 mm and 23.4 mm) and 1st (25.2 mm and 15.5 mm) percentiles after the 19th week of gestation, as shown in Fig. 3 . Table 1 shows the association between CL and PTD ≤ 34 + 6 gestational weeks. At 9–13 + 6 gestational weeks and CL ≤ the 50th percentile (36.0 mm), there was a negative correlation between CL and the incidence of PTD (all P < 0.05). After the 19th week of gestation, CL and PTD risk were negatively correlated for both gestational weeks when CL was less than or equal to the 75th percentile (all P the 75th percentile, the incidence of PTD gradually increased with decreasing CL, particularly for CL ≤ the 1st percentile, where the incidence of PTD increased multiple (19–23 + 6 weeks: 4.5% and 8.7%; 29–33 + 6 weeks: 12.9% and 37.3%). Table 1 Relationship between CL and PTD ≤ 34 + 6 weeks in each gestational week range. CL > the 75th percentile CL ≤ the 75th percentile CL ≤ the 50th percentile CL ≤ the 25th percentile CL ≤ the 10th percentile CL ≤ the 5th percentile CL ≤ the 1st percentile 9–13 + 6 weeks PTD ≤ 34 + 6 weeks 15/906 (1.7%) 61/2,862 (2.1%) 39/1,899 (2.1%) 21/971 (2.2%) 9/397 (2.3%) 5/213 (2.3%) 2/41 (4.9%) OR (95% CI) 0.782 (0.570–1.072) 0.959 (0.887–1.037) 0.911 (0.838–0.990) 0.876 (0.801–0.959) 0.853 (0.768–0.947) 0.838 (0.744–0.944) 0.803 (0.662–0.974) P 0.127 0.292 0.028 < 0.01 < 0.01 < 0.01 0.026 \(\chi\) 2 - 0.788 0.515 0.641 0.571 0.470 2.310 P - 0.375 0.473 0.423 0.450 0.563 0.165 19–23 + 6 weeks PTD ≤ 34 + 6 weeks 41/3,630 (1.1%) 193/10,900 (1.8%) 160/7,326 (2.2%) 102/3,653 (2.8%) 57/1,493 (3.8%) 33/738 (4.5%) 13/149 (8.7%) OR (95% CI) 1.125 (1.043–1.214) 0.888 (0.864–0.913) 0.894 (0.865–0.924) 0.892 (0.857–0.929) 0.897 (0.854–0.942) 0.886 (0.836–0.938) 0.887 (0.816–0.965) P < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 \(\chi\) 2 - 7.065 14.988 26.151 40.747 41.132 58.620 P - < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 29–33 + 6 weeks PTD ≤ 34 + 6 weeks 39/3,470 (1.1%) 247/10,775 (2.3%) 202/7,134 (2.8%) 154/3,671 (4.2%) 117/1,430 (8.2%) 93/721 (12.9%) 53/142 (37.3%) OR (95% CI) 1.004 (0.919–1.098) 0.860 (0.847–0.874) 0.846 (0.830–0.861) 0.830 (0.811–0.850) 0.827 (0.801–0.853) 0.815 (0.782–0.850) 0.778 (0.705–0.859) P 0.923 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 \(\chi\) 2 - 18.213 30.648 63.981 163.660 271.331 720.199 P - < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 PTD: Preterm delivery; CL: Cervical length; OR: Odds ratio; 95% CI: 95% confident interval. The associations between CL and PTD < 37 gestational weeks are shown in Table 2 . At 9–13 + 6 , 19–23 + 6 and 29–33 + 6 weeks, CL was negatively associated with the incidence of PTD when CL was ≤ the 75th percentile (all P the 75th percentile, the incidence of PTD gradually increased with decreasing CL, particularly for CL ≤ the 1st percentile, where the incidence of PTD significantly increased (9–13 + 6 weeks: 6.6% and 14.6%; 19–23 + 6 weeks: 11.2% and 23.5%; 29–33 + 6 weeks: 24.1% and 62.7%). Table 2 Relationship between CL and PTD the 75th percentile CL ≤ the 75th percentile CL ≤ the 50th percentile CL ≤ the 25th percentile CL ≤ the 10th percentile CL ≤ the 5th percentile CL ≤ the 1st percentile 9–13 + 6 weeks PTD < 37 weeks 41/906 (4.5%) 161/2,862 (5.6%) 119/1,899 (6.3%) 61/971 (6.3%) 26/397 (6.5%) 14/213 (6.6%) 6/41 (14.6%) OR (95% CI) 1.029 (0.909–1.165) 0.931 (0.888–0.975) 0.931 (0.876–0.990) 0.890 (0.823–0.962) 0.860 (0.778–0.950) 0.840 (0.748–0.945) 0.851 (0.730–0.991) P 0.653 < 0.01 0.023 < 0.01 < 0.01 < 0.01 0.038 \(\chi\) 2 - 1.641 3.457 2.815 2.318 1.547 8.498 P - 0.2 0.063 0.093 0.128 0.214 0.013 19–23 + 6 weeks PTD < 37 weeks 140/3,630 (3.9%) 543/10,900 (5.0%) 411/7,326 (5.6%) 246/3,653 (6.7%) 134/1,493 (9.0%) 83/738 (11.2%) 35/149 (23.5%) OR (95% CI) 1.039 (0.988–1.093) 0.904 (0.886–0.921) 0.890 (0.868–0.912) 0.871 (0.843–0.900) 0.865 (0.828–0.903) 0.852 (0.807–0.900) 0.875 (0.804–0.952) P 0.136 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 \(\chi\) 2 - 7.692 15.624 30.035 54.748 69.134 124.919 P - < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 29–33 + 6 weeks PTD < 37 weeks 141/3,470 (4.1%) 627/10,775 (5.8%) 492/7,134 (6.9%) 349/3,671 (9.5%) 230/1,430 (16.1%) 174/721 (24.1%) 89/142 (62.7%) OR (95% CI) 1.034 (0.988–1.081) 0.880 (0.870–0.890) 0.862 (0.850–0.874) 0.844 (0.828–0.860) 0.823 (0.799–0.847) 0.803 (0.770–0.837) 0.825 (0.744–0.916) P 0.148 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 \(\chi\) 2 - 15.861 33.383 82.709 209.089 345.917 786.044 P - < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 PTD: Preterm delivery; CL: Cervical length; OR: Odds ratio; 95% CI: 95% confident interval. Currently, the definition of a short cervix is CL < 25 mm, based on the 10th percentile derived from the 1996 study by Lams JD et al [ 8 ]. In light of this, we conducted a comparative analysis of the incidence of PTD < 37 gestational weeks in pregnant women with CL at or below the 5th, 4th, 3rd, 2nd and 1st percentiles, with those at or below the 10th percentile or less than 25 mm. As shown in Table 3 , the 1st percentile of CL exceeded 25 mm at both 9–13 + 6 and 19–23 + 6 gestational weeks. A significantly increased incidence of PTD < 37 gestational weeks was evident among women with CL ≤ 29.5 mm (the 4th percentile) at 19–23 + 6 gestational weeks, as compared with those with CL ≤ the 10th percentile at that time. Compared with that in women with CL ≤ the 10th percentile, the incidence of PTD < 37 gestational weeks among women with CL ≤ 23.4 mm (the 5th percentile) increased notably at 29–33 + 6 gestational weeks. We observed no significant difference in the incidence of PTD < 37 gestational weeks between women with CL ≤ 25 mm and those with CL ≤ 23.4 mm (the 5th percentile, P = 0.169), and a significantly higher incidence of PTD < 37 gestational weeks was noted in women with CL ≤ 22.3 mm (the 4th percentile, P < 0.01). Table 3 Comparison of PTD incidence in women with CL at or below the 5th percentile with those ≤ the 10th percentile or 25 mm CL ≤ the 10th percentile CL ≤ 25 mm CL ≤ the 5th percentile CL ≤ the 4th percentile CL ≤ the 3rd percentile CL ≤ the 2nd percentile CL ≤ the 1st percentile CL 31.4 mm 25 mm 30.5 mm 30.2 mm 30.0 mm 29.3 mm 27.9 mm 9–13 + 6 weeks PTD < 37 weeks 26/397 (6.5%) 3/10 (30.0%) 14/213 (6.6%) 12/156 (7.7%) 9/119 (7.6%) 7/75 (9.3%) 6/41 (14.6%) \(\chi\) 2 ( P ) a - - 0.0 (0.991) 0.229 (0.632) 0.149 (0.700) 0.752 (0.386) 3.587 (0.104) \(\chi\) 2 ( P ) b - - - - - - - CL 31.5 mm 25 mm 30.0 mm 29.5 mm 28.7 mm 27.5 mm 25.2 mm 19–23 + 6 weeks PTD < 37 weeks 134/1,493 (9.0%) 33/138 (23.9%) 83/738 (11.2%) 73/590 (12.4%) 63/455 (13.8%) 51/292 (17.5%) 35/149 (23.5%) \(\chi\) 2 ( P ) a - - 2.902 (0.088) 5.455 ( 0.020 ) 9.102 ( < 0.01 ) 18.952 ( < 0.01 ) 30.913 ( < 0.01 ) \(\chi\) 2 ( P ) b - - - - - - - CL 27.1 mm 25 mm 23.4 mm 22.3 mm 20.8 mm 19.2 mm 15.5 mm 29–33 + 6 weeks PTD < 37 weeks 230/1,430 (16.1%) 192/903 (21.3%) 174/721 (24.1%) 158/577 (27.4%) 142/427 (33.3%) 118/289 (40.8%) 89/142 (62.7%) \(\chi\) 2 ( P ) a - - 20.359 ( < 0.01 ) 33.656 ( < 0.01 ) 60.522 ( < 0.01 ) 91.185 ( < 0.01 ) 173.365 ( < 0.01 ) \(\chi\) 2 ( P ) b - 1.892 (0.169) 7.304 ( < 0.01 ) 32.044 ( < 0.01 ) 43.564 ( < 0.01 ) 107.048 ( < 0.01 ) a Compared with CL ≤ the 10th percentile; b Compared with CL ≤ 25 mm; CL: Cervical length; PTD: Preterm delivery. Discussion The results in the present study showed a progressive decrease in CL with increasing gestational age, that the ability of CL to predict PTD was enhanced after the 19th week of gestation, and that the defining threshold of a short cervix should probably be less than 25 mm after the 29th gestational week. A previous investigation [ 13 ] demonstrated that the median CL remained statistically invariant between the 8th and 20th gestational weeks, and a trend toward progressive CL shortening was evident with advancing gestational age after the 20th gestational week, with an accelerated rate of reduction as the time of delivery approached. Consistent with the previous findings, the results of this study indicated a gradual decrease in CL as gestational age increased. In addition, the rate of CL shortening between 19–23 + 6 and 29–33 + 6 weeks was significantly higher than that between 9–13 + 6 and 19–23 + 6 weeks, with pronounced differences observed specifically at the 10th, 5th and 1st percentiles. This finding suggested that the CL is an indicator of continuous variation throughout pregnancy and that a gestational age-specific standard for defining a short cervix is needed. The present study revealed no significant correlation between CL at 9–13 + 6 weeks and PTD ≤ 34 + 6 gestational weeks. Moreover, compared with the incidence of PTD in women with CL > the 75th percentile, there was no significant difference observed in women whose CL was equal to or less than each percentile. Previous investigations [ 6 , 15 – 21 ] have indicated that the conventional single-line method [ 6 ] of CL measurement for PTD screening is controversial. This controversy stems potentially from the curved cervix during the first trimester [ 6 ], which may also lead to the findings shown in this study. To develop a more accurate and stable model for predicting PTD by the CL in the first trimester, other clinical indicators and maternal characteristics, such as shear-wave elastography and PTD history, may need to be considered [ 6 , 18 ]. At 19–23 + 6 gestational weeks, the median CL was 37.4 mm (interquartile range, 34.1–40.8 mm) in the present study, which is similar to that reported in previous analyses [ 14 ] in which the median CL was 36 mm (interquartile range, 35–40 mm) in the second trimester. To date, several studies [ 5 , 14 , 22 ] have shown a significant correlation between CL assessed during the second trimester and the subsequent risk of preterm birth. ROC analysis conducted in this study indicated a significant correlation between CL measured at 19–23 + 6 gestational weeks and the incidences of PTD ≤ 34 + 6 gestational weeks and the 75th percentile. Universal CL screening during the second trimester and vaginal progesterone therapy for women diagnosed with a short cervix have been found to significantly mitigate the risk of subsequent PTD [ 11 , 22 – 25 ]. Currently, studies on the use of third-trimester CL as a predictive factor for PTD are lacking. However, the detection of cervical shortening prior to the 34th gestational week and the implementation of efficacious interventions for the management of women with short cervix are assumed to be important for reducing PTD < 37 gestational weeks [ 7 ]. The results of this study showed that CL at 29–33 + 6 gestational weeks was significantly decreased and more significantly associated with PTD than was CL in the second trimester. In addition, the current definition of a short cervix is CL < 25 mm [ 8 – 11 ]. The incidence of PTD across each trimester increased when the CL was at or below the 1st percentile compared to the 5th percentile, and the CL in the 1st percentile at 29–33 + 6 gestational weeks was 15.5 mm. The incidence of PTD < 37 gestational weeks was significantly higher in women with CL ≤ 22.3 mm at 29–33 + 6 gestational weeks than in women with CL ≤ 25 mm. Similarly, Tsakiridis et al. reported that third - trimester CL alone could predict 17% of late PTD (delivery at 34–36 weeks), corresponding to a CL of 22 mm [ 7 ]. Therefore, the appropriate CL threshold in the third trimester for predicting PTD should probably be lower than 25 mm. The advantage of the present study lies in the comparative analysis of CL variations across the first, second and third trimesters and the association with PTD. Additionally, the large sample size employed in this study confers a degree of reliability to the findings. This study has several limitations. First, the number of women providing CL data from the first trimester was limited in scope. Second, this retrospective study analyzed CL measurements from the first, second and third trimesters separately. To augment the sample size, cases lacking CL data for a particular trimester were not excluded; thus, this study was not a continuous analysis of the same population. Consequently, the predictive contribution of CL measurements taken during the first, second and third trimesters to PTD, as well as the determination of the most appropriate threshold values, necessitates further investigation through prospective studies with larger sample populations. Conclusions CL progressively decreases with increasing gestational age and has emerged as a more potent predictor of PTD after the 19th week of gestation. The defining threshold of a short cervix should probably be less than 25 mm at 29–33 + 6 gestational weeks. Abbreviations CL cervical length PTD preterm delivery ROC receiver operating characteristic AUC area under the curve Declarations Ethics approval and consent to participate This study was approved by the Clinical Research Ethics Committee of Peking University First Hospital [No. 2023 (123-001)], and all participants signed informed written consent forms for their clinical records to be used in this study. Consent for publication Not Applicable. Availability of data and materials The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions. Competing interests The authors declare no conflict of interest. Funding This study was supported by the National Key Research and Development Program (Grant No. 2022YFC2704605) to Yumei Wei. Authors' contributions This study was conceived and designed by Yumei Wei. The data was collected by Qidi Zhang, Xinyue Han and Yuchun Zhu with the support of Huixia Yang. The data was analyzed by Qidi Zhang, Xinyue Han and Yumei Wei. The paper was written by Qidi Zhang and Yumei Wei. Acknowledgements We thank the obstetricians involved in the project for collecting and analysing the data. And we appreciate all participating pregnant women for providing personal information. References S. R. Walani. Global burden of preterm birth. Int J Gynaecol Obstet. 2020;150(1):31-33. J. Perin, A. Mulick, D. Yeung, F. Villavicencio, G. Lopez, K. L. Strong, D. Prieto-Merino, S. Cousens, R. E. Black and L. Liu. Global, regional, and national causes of under-5 mortality in 2000-19: an updated systematic analysis with implications for the Sustainable Development Goals. Lancet Child Adolesc Health. 2022;6(2):106-115. W. H. Organization. WHO recommendations on interventions to improve preterm birth outcomes. 2015; E. O. Ohuma, A. B. Moller, E. Bradley, S. Chakwera, L. Hussain-Alkhateeb, A. Lewin, Y. B. Okwaraji, W. R. Mahanani, E. W. Johansson, T. Lavin, et al. National, regional, and global estimates of preterm birth in 2020, with trends from 2010: a systematic analysis. Lancet. 2023;402(10409):1261-1271. T. Wikstrom, H. Hagberg, B. Jacobsson, P. Kuusela, J. Wesstrom, P. Lindgren, H. Fadl, U. B. Wennerholm and L. Valentin. Effect of second-trimester sonographic cervical length on the risk of spontaneous preterm delivery in different risk groups: A prospective observational multicenter study. Acta Obstet Gynecol Scand. 2021;100(9):1644-1655. Q. Feng, P. Chaemsaithong, H. Duan, X. Ju, K. Appiah, L. Shen, X. Wang, Y. Tai, T. Y. Leung and L. C. Poon. Screening for spontaneous preterm birth by cervical length and shear-wave elastography in the first trimester of pregnancy. Am J Obstet Gynecol. 2022;227(3):500 e1-500 e14. I. Tsakiridis, T. Dagklis, A. Sotiriadis, A. Mamopoulos, L. Zepiridis and A. Athanasiadis. Third-trimester cervical length assessment for the prediction of spontaneous late preterm birth. J Matern Fetal Neonatal Med. 2023;36(1):2201368. J. D. Iams, R. L. Goldenberg, P. J. Meis, B. M. Mercer, A. Moawad, A. Das, E. Thom, D. McNellis, R. L. Copper, F. Johnson, et al. The Length of the Cervix and the Risk of Spontaneous Premature Delivery. New England Journal of Medicine. 1996;334(9):567-573. J. Visintine, V. Berghella, D. Henning and J. Baxter. Cervical length for prediction of preterm birth in women with multiple prior induced abortions. Ultrasound Obstet Gynecol. 2008;31(2):198-200. Prediction and Prevention of Spontaneous Preterm Birth: ACOG Practice Bulletin, Number 234. Obstet Gynecol. 2021;138(2):e65-e90. R. Maymon, M. Pekar-Zlotin, H. Meiri, Z. Haklai, E. S. Gordon, G. Shlichkov and H. Cuckle. Change in prevalence of preterm birth in Israel following publication of national guidelines recommending routine sonographic cervical-length measurement at 19-25 weeks' gestation. Ultrasound Obstet Gynecol. 2023;61(5):610-616. C. B. Wulff, L. Rode, S. Rosthoj, E. Hoseth, O. B. Petersen and A. Tabor. Transvaginal sonographic cervical length in first and second trimesters in a low-risk population: a prospective study. Ultrasound Obstet Gynecol. 2018;51(5):604-613. D. W. Gudicha, R. Romero, D. Kabiri, E. Hernandez-Andrade, P. Pacora, O. Erez, J. P. Kusanovic, E. Jung, C. Paredes, S. M. Berry, et al. Personalized assessment of cervical length improves prediction of spontaneous preterm birth: a standard and a percentile calculator. Am J Obstet Gynecol. 2021;224(3):288 e1-288 e17. R. K. Ross, S. R. Cole, D. Westreich, J. K. Edwards, P. Musonda, B. Vwalika, M. P. Kasaro, J. T. Price and J. S. A. Stringer. Different effects for different questions: An illustration using short cervix and the risk of preterm birth. Int J Gynaecol Obstet. 2023;160(3):842-849. P. Antsaklis, G. Daskalakis, A. Pilalis, N. Papantoniou, S. Mesogitis and A. Antsaklis. The role of cervical length measurement at 11-14 weeks for the prediction of preterm delivery. J Matern Fetal Neonatal Med. 2011;24(3):465-70. E. Greco, A. Lange, F. Ushakov, J. R. Calvo and K. H. Nicolaides. Prediction of spontaneous preterm delivery from endocervical length at 11 to 13 weeks. Prenat Diagn. 2011;31(1):84-9. A. P. Souka, I. Papastefanou, V. Michalitsi, K. Salambasis, C. Chrelias, G. Salamalekis and D. Kassanos. Cervical length changes from the first to second trimester of pregnancy, and prediction of preterm birth by first-trimester sonographic cervical measurement. J Ultrasound Med. 2011;30(7):997-1002. E. Greco, R. Gupta, A. Syngelaki, L. C. Poon and K. H. Nicolaides. First-trimester screening for spontaneous preterm delivery with maternal characteristics and cervical length. Fetal Diagn Ther. 2012;31(3):154-61. N. Sananes, N. Meyer, A. Gaudineau, G. Aissi, E. Boudier, G. Fritz, B. Viville, I. Nisand, B. Langer and R. Favre. Prediction of spontaneous preterm delivery in the first trimester of pregnancy. Eur J Obstet Gynecol Reprod Biol. 2013;171(1):18-22. M. Parra-Cordero, A. Sepúlveda-Martínez, G. Rencoret, E. Valdés, D. Pedraza and H. Muñoz. Is there a role for cervical assessment and uterine artery Doppler in the first trimester of pregnancy as a screening test for spontaneous preterm delivery? Ultrasound Obstet Gynecol. 2014;43(3):291-6. O. Weitzner, T. Biron-Shental, Y. Daykan, O. Ezra and O. Markovitch. Can sonographic measurements and changes in cervical length during pregnancy predict preterm labour in an asymptomatic low-risk population? J Matern Fetal Neonatal Med. 2019;32(13):2107-2112. A. Figarella, C. Chau, A. Loundou, C. d'Ercole and F. Bretelle. The introduction of a universal transvaginal cervical length screening program is associated with a reduced preterm birth rate. Am J Obstet Gynecol. 2023;228(2):219.e1-219.e14. S. Parry, H. Simhan, M. Elovitz and J. Iams. Universal maternal cervical length screening during the second trimester: pros and cons of a strategy to identify women at risk of spontaneous preterm delivery. Am J Obstet Gynecol. 2012;207(2):101-6. A. P. Souka, I. Papastefanou, A. Pilalis, D. Kassanos and G. Papadopoulos. Implementation of universal screening for preterm delivery by mid-trimester cervical-length measurement. Ultrasound Obstet Gynecol. 2019;53(3):396-401. E. Hernandez-Andrade, E. S. Huntley, B. Sibai, S. C. Blackwell and E. E. Soto-Torres. A reduction in cervical length after starting vaginal progesterone in women with short cervix is significantly associated with preterm delivery </=34 weeks and <37 weeks of gestation. Ultrasound Obstet Gynecol. 2023; Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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-4005959","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":278244026,"identity":"3695456f-acb6-4e25-b045-6339e6c4cb18","order_by":0,"name":"Qidi Zhang","email":"","orcid":"","institution":"Peking University First Hospital","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Qidi","middleName":"","lastName":"Zhang","suffix":""},{"id":278244027,"identity":"7d0fdc8d-a51a-484d-8979-18f7a72b8a56","order_by":1,"name":"Xinyue Han","email":"","orcid":"","institution":"Peking University First Hospital","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xinyue","middleName":"","lastName":"Han","suffix":""},{"id":278244028,"identity":"a0988928-fbfa-4d4d-bce8-e9c89952da7f","order_by":2,"name":"Huixia Yang","email":"","orcid":"","institution":"Peking University First Hospital","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Huixia","middleName":"","lastName":"Yang","suffix":""},{"id":278244029,"identity":"7f86f977-560f-4d84-86e8-5785bb5bef3c","order_by":3,"name":"Yuchun Zhu","email":"","orcid":"","institution":"Peking University First Hospital","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yuchun","middleName":"","lastName":"Zhu","suffix":""},{"id":278244030,"identity":"2d9b31ea-001a-48bb-bcbb-11adbaf4a0ac","order_by":4,"name":"Yumei Wei","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7ElEQVRIiWNgGAWjYBACgwOMDSCah429+eCDDwY2csRr4eM5lmw4oyDNmAgtUIacRI6ZNM+Hw4mEtRxvbpPmzbGRYZNIS5C2MWBOYGA/fHQDPi1mZw4CtWxL42HjeXzAOMeALY+BJy3tBl4tNxJBWg4DvZ+WkJxjwFPMIMFjhl/L/YcgLf952BhyDA5bGEgkNhDSYn+DEaTlAA8bR45hM4OBAWEtlmcSmy3nbksG+uVYMmOPQYIxGyG/GBw//vDG22129vLtzcd//PjzX46f/fAxvFqAgEUChctGQDkIMH8gQtEoGAWjYBSMZAAANl9KpLVopyIAAAAASUVORK5CYII=","orcid":"","institution":"Peking University First Hospital","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Yumei","middleName":"","lastName":"Wei","suffix":""}],"badges":[],"createdAt":"2024-03-02 08:46:10","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4005959/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4005959/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52541414,"identity":"718fafac-b91f-4c71-939e-fdac8ef7ef32","added_by":"auto","created_at":"2024-03-12 17:32:04","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":4169153,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart of the population in this study. PTD, preterm delivery.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-4005959/v1/5e460ef08a0116ae68d4cd03.png"},{"id":52541413,"identity":"432130d4-e661-4575-9bc0-98e3891add2b","added_by":"auto","created_at":"2024-03-12 17:32:04","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2454796,"visible":true,"origin":"","legend":"\u003cp\u003eArea under the curve (AUC) of the receiver operating characteristic (ROC) according to gestational week.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-4005959/v1/8e26fd37878eb84335472c4b.png"},{"id":52541415,"identity":"e9a66b20-0eab-4100-aa38-f5172f3d323e","added_by":"auto","created_at":"2024-03-12 17:32:05","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2393369,"visible":true,"origin":"","legend":"\u003cp\u003eThe cervical lengths at the 75th, 50th, 25th, 10th, 5th and 1st percentiles according to gestational week.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-4005959/v1/5514a11f451ca17274f3a6ca.png"},{"id":77741611,"identity":"28c8f6fb-bd03-489c-874d-764b67f88e30","added_by":"auto","created_at":"2025-03-05 05:41:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9476094,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4005959/v1/b20ff0c7-d357-4e15-a5c5-512faa39875b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Alteration and Predictive Ability of Cervical Length for Preterm Delivery in Each Gestational Trimester","fulltext":[{"header":"Introduction","content":"\u003cp\u003eComplications of preterm delivery (PTD) before 37 gestational weeks are the primary cause of mortality among children under 5 years of age globally [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], as a result of respiratory disorder, feeding difficulty, impaired temperature regulation and increased risk of infection [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The global incidence of PTD presents an increase between 2010 and 2020, this issue continues to affect the health of children worldwide and it is crucial to reduce the incidence of PTD [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCervical length (CL) ascertained by ultrasound has consistently emerged as a prominent predictor of PTD. Several previous studies have shown a significant correlation between CL during the first, second and third trimesters of pregnancy and the incidence of PTD [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Based on the seminal research by Lams JD et al. in 1996, the prevailing definition of a short cervix is CL\u0026thinsp;\u0026lt;\u0026thinsp;25 mm [\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Several studies [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] have shown that the incidence of PTD is significantly higher in pregnant women with CL\u0026thinsp;\u0026lt;\u0026thinsp;25 mm than in those without short cervix; these studies employed CL measurements obtained from the first, second and third trimesters of pregnancy.\u003c/p\u003e \u003cp\u003eHowever, importantly, the CL is a dynamic parameter that continuously changes with increasing gestational age. Previous work has shown a marked reduction in CL during the third trimester compared to the first and second trimesters [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Consequently, employing the cut-off value of 25 mm to delineate the short cervix across varying gestational weeks may not be entirely accurate.\u003c/p\u003e \u003cp\u003eIn the present study, we aimed to investigate the role of CL as a predictor for PTD at distinct gestational weeks by examining alterations in CL throughout different gestational periods and subsequently comparing the incidence of PTD at or below every percentile of CL within each trimester.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eStudy sample\u003c/h3\u003e\n\u003cp\u003e In this study, a total of 36,320 CL measurements were obtained from the medical records of 17,756 pregnant women who delivered singleton live births between January 1, 2020, and October 31, 2023, at Peking University First Hospitals in Beijing. In total, 263 pregnant women (601 measurements) were excluded because of the coexistence of PTD and uterine rupture (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;11), a low-lying placenta with hemorrhage (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;3), eclampsia (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;202), or placental abruption (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;47). And 1,141 women (3,176 measurements) were excluded due to a diagnosis of threatened preterm labor (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;685), shortened CL (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;230), or operation via cerclage (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;226). A total of 16,352 patients (32,543 measurements) were ultimately included in the primary analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e): 3,768 measurements at 9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks, 14,530 measurements at 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks, and 14,245 measurements at 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks.\u003c/p\u003e\n\u003ch3\u003eUltrasound assessment and pregnancy outcomes\u003c/h3\u003e\n\u003cp\u003eData on CL were extracted from ultrasound reports obtained during pregnancy based on measurements performed by trained obstetricians using standardized methods and criteria. The CL of all pregnant women were assessed using the single-line method [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], which measures the linear distance between the internal and external cervical os (the two endpoints of the glandular area surrounding the endocervical canal).\u003c/p\u003e \u003cp\u003eThe primary pregnancy outcome in this study was PTD, which included PTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and \u0026lt;\u0026thinsp;37 gestational weeks.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eThe analyses in this study were conducted with SPSS software (IBM SPSS Statistics 26.0). Based on a single-sample Kolmogorov-Smirnov test, continuous variables that were not normally distributed are presented as the median (25th-75th percentile), and categorical variables are presented as numbers and percentages. The associations between CL at various gestational weeks and PTD were evaluated using receiver operating characteristic (ROC) curves and logistic regression analysis. The chi-square test was used for comparisons of the incidence of PTD between patients at or below each percentile for CL with those with CL above the 75th percentile [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 indicated that the differences were statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eA total of 328 (2.0%) of the 16,352 participants had PTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks, and 870 (5.3%) had PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks. The medians (25th-75th percentile) for maternal age, gestational age, gravidity, parity and predelivery weight were 32.0 (30.0\u0026ndash;35.0) years, 39.3 (38.6\u0026ndash;40.1) weeks, 1.0 (1.0\u0026ndash;2.0), 1.0 (1.0\u0026ndash;1.0) and 70.0 (64.0\u0026ndash;77.0) kg, respectively. A total of 10,060 (61.5%) women gave birth by vaginal delivery, and the remaining 6,292 (38.5%) underwent cesarean section.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the area under the curve (AUC) of the ROC, which indicates the predictive value of CL for PTD. As gestational age advanced, the predictive value of CL for PTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks increased, and these associations were significant after the 19th week of pregnancy (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). The AUC and 95% confidence interval (95% CI) at 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e and 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks increased gradually, with corresponding values of 0.615 (0.576\u0026ndash;0.655) and 0.694 (0.658\u0026ndash;0.730), respectively. Starting from the 9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks of gestation, CL demonstrated a significant predictive value for PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), accompanied by a progressive increase in the AUC. The AUC (95% CI) values at 9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e, 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e and 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks were 0.543 (0.502\u0026ndash;0.584), 0.576 (0.553-0.600) and 0.632 (0.609\u0026ndash;0.655), respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWith increasing gestational age, a downward trend in CL was observed at each percentile, with a particularly obvious decrease at the 10th (31.5 mm and 27.1 mm), 5th (30.0 mm and 23.4 mm) and 1st (25.2 mm and 15.5 mm) percentiles after the 19th week of gestation, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the association between CL and PTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks. At 9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks and CL\u0026thinsp;\u0026le;\u0026thinsp;the 50th percentile (36.0 mm), there was a negative correlation between CL and the incidence of PTD (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). After the 19th week of gestation, CL and PTD risk were negatively correlated for both gestational weeks when CL was less than or equal to the 75th percentile (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). In comparison to CL\u0026thinsp;\u0026gt;\u0026thinsp;the 75th percentile, the incidence of PTD gradually increased with decreasing CL, particularly for CL\u0026thinsp;\u0026le;\u0026thinsp;the 1st percentile, where the incidence of PTD increased multiple (19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks: 4.5% and 8.7%; 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks: 12.9% and 37.3%).\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\u003eRelationship between CL and PTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks in each gestational week range.\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=\"left\" 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\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026gt;\u0026thinsp;the 75th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 75th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 50th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 25th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 10th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 5th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 1st percentile\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003e9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15/906 (1.7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e61/2,862 (2.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e39/1,899 (2.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e21/971 (2.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e9/397 (2.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e5/213 (2.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e2/41 (4.9%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR (95% CI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.782 (0.570\u0026ndash;1.072)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.959 (0.887\u0026ndash;1.037)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.911 (0.838\u0026ndash;0.990)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.876 (0.801\u0026ndash;0.959)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.853 (0.768\u0026ndash;0.947)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.838 (0.744\u0026ndash;0.944)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.803 (0.662\u0026ndash;0.974)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.127\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.292\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e0.028\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e0.026\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.788\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.515\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.641\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.571\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.470\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e2.310\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e-\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.375\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.473\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.423\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.450\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.563\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.165\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003e19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e41/3,630 (1.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e193/10,900 (1.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e160/7,326 (2.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e102/3,653 (2.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e57/1,493 (3.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e33/738 (4.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e13/149 (8.7%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR (95% CI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.125 (1.043\u0026ndash;1.214)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.888 (0.864\u0026ndash;0.913)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.894 (0.865\u0026ndash;0.924)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.892 (0.857\u0026ndash;0.929)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.897 (0.854\u0026ndash;0.942)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.886 (0.836\u0026ndash;0.938)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.887 (0.816\u0026ndash;0.965)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e7.065\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e14.988\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e26.151\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e40.747\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e41.132\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e58.620\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003e29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e39/3,470 (1.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e247/10,775 (2.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e202/7,134 (2.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e154/3,671 (4.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e117/1,430 (8.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e93/721 (12.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e53/142 (37.3%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR (95% CI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.004 (0.919\u0026ndash;1.098)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.860 (0.847\u0026ndash;0.874)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.846 (0.830\u0026ndash;0.861)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.830 (0.811\u0026ndash;0.850)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.827 (0.801\u0026ndash;0.853)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.815 (0.782\u0026ndash;0.850)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.778 (0.705\u0026ndash;0.859)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.923\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e18.213\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30.648\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e63.981\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e163.660\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e271.331\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e720.199\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003ePTD: Preterm delivery; CL: Cervical length; OR: Odds ratio; 95% CI: 95% confident interval.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe associations between CL and PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. At 9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e, 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e and 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks, CL was negatively associated with the incidence of PTD when CL was \u0026le;\u0026thinsp;the 75th percentile (all \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In comparison to that of CL\u0026thinsp;\u0026gt;\u0026thinsp;the 75th percentile, the incidence of PTD gradually increased with decreasing CL, particularly for CL\u0026thinsp;\u0026le;\u0026thinsp;the 1st percentile, where the incidence of PTD significantly increased (9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks: 6.6% and 14.6%; 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks: 11.2% and 23.5%; 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks: 24.1% and 62.7%).\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\u003eRelationship between CL and PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 weeks in each gestational week range.\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=\"left\" 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\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026gt;\u0026thinsp;the 75th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 75th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 50th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 25th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 10th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 5th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 1st percentile\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003e9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePTD \u0026lt;\u0026nbsp;37 weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e41/906 (4.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e161/2,862 (5.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e119/1,899 (6.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e61/971 (6.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e26/397 (6.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e14/213 (6.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e6/41 (14.6%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR (95% CI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.029 (0.909\u0026ndash;1.165)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.931 (0.888\u0026ndash;0.975)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.931 (0.876\u0026ndash;0.990)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.890 (0.823\u0026ndash;0.962)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.860 (0.778\u0026ndash;0.950)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.840 (0.748\u0026ndash;0.945)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.851 (0.730\u0026ndash;0.991)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.653\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e0.023\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e0.038\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.641\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.457\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.815\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2.318\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e1.547\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e8.498\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.063\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.093\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.128\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.214\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e0.013\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003e19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePTD \u0026lt;\u0026nbsp;37 weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e140/3,630 (3.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e543/10,900 (5.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e411/7,326 (5.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e246/3,653 (6.7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e134/1,493 (9.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e83/738 (11.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e35/149 (23.5%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR (95% CI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.039 (0.988\u0026ndash;1.093)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.904 (0.886\u0026ndash;0.921)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.890 (0.868\u0026ndash;0.912)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.871 (0.843\u0026ndash;0.900)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.865 (0.828\u0026ndash;0.903)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.852 (0.807\u0026ndash;0.900)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.875 (0.804\u0026ndash;0.952)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.136\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e7.692\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e15.624\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e30.035\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e54.748\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e69.134\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e124.919\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003e29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePTD \u0026lt;\u0026nbsp;37 weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e141/3,470 (4.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e627/10,775 (5.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e492/7,134 (6.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e349/3,671 (9.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e230/1,430 (16.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e174/721 (24.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e89/142 (62.7%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR (95% CI)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.034 (0.988\u0026ndash;1.081)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.880 (0.870\u0026ndash;0.890)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.862 (0.850\u0026ndash;0.874)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.844 (0.828\u0026ndash;0.860)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.823 (0.799\u0026ndash;0.847)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.803 (0.770\u0026ndash;0.837)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.825 (0.744\u0026ndash;0.916)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.148\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e15.861\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e33.383\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e82.709\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e209.089\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e345.917\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e786.044\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003ePTD: Preterm delivery; CL: Cervical length; OR: Odds ratio; 95% CI: 95% confident interval.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eCurrently, the definition of a short cervix is CL\u0026thinsp;\u0026lt;\u0026thinsp;25 mm, based on the 10th percentile derived from the 1996 study by Lams JD et al [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In light of this, we conducted a comparative analysis of the incidence of PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks in pregnant women with CL at or below the 5th, 4th, 3rd, 2nd and 1st percentiles, with those at or below the 10th percentile or less than 25 mm.\u003c/p\u003e \u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the 1st percentile of CL exceeded 25 mm at both 9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e and 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks. A significantly increased incidence of PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks was evident among women with CL\u0026thinsp;\u0026le;\u0026thinsp;29.5 mm (the 4th percentile) at 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks, as compared with those with CL\u0026thinsp;\u0026le;\u0026thinsp;the 10th percentile at that time. Compared with that in women with CL\u0026thinsp;\u0026le;\u0026thinsp;the 10th percentile, the incidence of PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks among women with CL\u0026thinsp;\u0026le;\u0026thinsp;23.4 mm (the 5th percentile) increased notably at 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks. We observed no significant difference in the incidence of PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks between women with CL\u0026thinsp;\u0026le;\u0026thinsp;25 mm and those with CL\u0026thinsp;\u0026le;\u0026thinsp;23.4 mm (the 5th percentile, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.169), and a significantly higher incidence of PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks was noted in women with CL\u0026thinsp;\u0026le;\u0026thinsp;22.3 mm (the 4th percentile, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01).\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\u003eComparison of PTD incidence in women with CL at or below the 5th percentile with those\u0026thinsp;\u0026le;\u0026thinsp;the 10th percentile or 25 mm\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=\"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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 10th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;25 mm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 5th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 4th percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 3rd percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 2nd percentile\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;the 1st percentile\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.4 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30.5 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e30.2 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e30.0 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e29.3 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e27.9 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePTD \u0026lt;\u0026nbsp;37 weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26/397 (6.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3/10 (30.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14/213 (6.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e12/156 (7.7%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e9/119 (7.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e7/75 (9.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6/41 (14.6%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e (\u003cem\u003eP\u003c/em\u003e)\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.0 (0.991)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.229 (0.632)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.149 (0.700)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.752 (0.386)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e3.587 (0.104)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e (\u003cem\u003eP\u003c/em\u003e)\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\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\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\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\u003eCL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.5 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30.0 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e29.5 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e28.7 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e27.5 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e25.2 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePTD \u0026lt;\u0026nbsp;37 weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e134/1,493 (9.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e33/138 (23.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e83/738 (11.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e73/590 (12.4%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e63/455 (13.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e51/292 (17.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e35/149 (23.5%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e (\u003cem\u003eP\u003c/em\u003e)\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.902 (0.088)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5.455 (\u003cb\u003e0.020\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e9.102 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e18.952 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e30.913 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e (\u003cem\u003eP\u003c/em\u003e)\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\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\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-\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\u003eCL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.1 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e23.4 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e22.3 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e20.8 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e19.2 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e15.5 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePTD \u0026lt;\u0026nbsp;37 weeks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e230/1,430 (16.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e192/903 (21.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e174/721 (24.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e158/577 (27.4%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e142/427 (33.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e118/289 (40.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e89/142 (62.7%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e (\u003cem\u003eP\u003c/em\u003e)\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20.359 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e33.656 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e60.522 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e91.185 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e173.365 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\chi\\)\u003c/span\u003e\u003c/span\u003e\u003csup\u003e2\u003c/sup\u003e (\u003cem\u003eP\u003c/em\u003e)\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.892 (0.169)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7.304 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e32.044 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e43.564 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e107.048 (\u003cb\u003e\u0026lt;\u0026nbsp;0.01\u003c/b\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003e\u003csup\u003ea\u003c/sup\u003eCompared with CL\u0026thinsp;\u0026le;\u0026thinsp;the 10th percentile; \u003csup\u003eb\u003c/sup\u003eCompared with CL\u0026thinsp;\u0026le;\u0026thinsp;25 mm; CL: Cervical length; PTD: Preterm delivery.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe results in the present study showed a progressive decrease in CL with increasing gestational age, that the ability of CL to predict PTD was enhanced after the 19th week of gestation, and that the defining threshold of a short cervix should probably be less than 25 mm after the 29th gestational week.\u003c/p\u003e \u003cp\u003eA previous investigation [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] demonstrated that the median CL remained statistically invariant between the 8th and 20th gestational weeks, and a trend toward progressive CL shortening was evident with advancing gestational age after the 20th gestational week, with an accelerated rate of reduction as the time of delivery approached. Consistent with the previous findings, the results of this study indicated a gradual decrease in CL as gestational age increased. In addition, the rate of CL shortening between 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e and 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks was significantly higher than that between 9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e and 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks, with pronounced differences observed specifically at the 10th, 5th and 1st percentiles. This finding suggested that the CL is an indicator of continuous variation throughout pregnancy and that a gestational age-specific standard for defining a short cervix is needed.\u003c/p\u003e \u003cp\u003eThe present study revealed no significant correlation between CL at 9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks and PTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks. Moreover, compared with the incidence of PTD in women with CL\u0026thinsp;\u0026gt;\u0026thinsp;the 75th percentile, there was no significant difference observed in women whose CL was equal to or less than each percentile. Previous investigations [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan additionalcitationids=\"CR16 CR17 CR18 CR19 CR20\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] have indicated that the conventional single-line method [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] of CL measurement for PTD screening is controversial. This controversy stems potentially from the curved cervix during the first trimester [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], which may also lead to the findings shown in this study. To develop a more accurate and stable model for predicting PTD by the CL in the first trimester, other clinical indicators and maternal characteristics, such as shear-wave elastography and PTD history, may need to be considered [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAt 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks, the median CL was 37.4 mm (interquartile range, 34.1\u0026ndash;40.8 mm) in the present study, which is similar to that reported in previous analyses [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] in which the median CL was 36 mm (interquartile range, 35\u0026ndash;40 mm) in the second trimester. To date, several studies [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] have shown a significant correlation between CL assessed during the second trimester and the subsequent risk of preterm birth. ROC analysis conducted in this study indicated a significant correlation between CL measured at 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks and the incidences of PTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks and \u0026lt;\u0026thinsp;37 gestational weeks. Furthermore, a notable increase in PTD incidence in women with CL equal to or below each percentile was observed compared to women with CL\u0026thinsp;\u0026gt;\u0026thinsp;the 75th percentile.\u003c/p\u003e \u003cp\u003eUniversal CL screening during the second trimester and vaginal progesterone therapy for women diagnosed with a short cervix have been found to significantly mitigate the risk of subsequent PTD [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan additionalcitationids=\"CR23 CR24\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Currently, studies on the use of third-trimester CL as a predictive factor for PTD are lacking. However, the detection of cervical shortening prior to the 34th gestational week and the implementation of efficacious interventions for the management of women with short cervix are assumed to be important for reducing PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The results of this study showed that CL at 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks was significantly decreased and more significantly associated with PTD than was CL in the second trimester.\u003c/p\u003e \u003cp\u003eIn addition, the current definition of a short cervix is CL\u0026thinsp;\u0026lt;\u0026thinsp;25 mm [\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The incidence of PTD across each trimester increased when the CL was at or below the 1st percentile compared to the 5th percentile, and the CL in the 1st percentile at 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks was 15.5 mm. The incidence of PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks was significantly higher in women with CL\u0026thinsp;\u0026le;\u0026thinsp;22.3 mm at 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks than in women with CL\u0026thinsp;\u0026le;\u0026thinsp;25 mm. Similarly, Tsakiridis et al. reported that third - trimester CL alone could predict 17% of late PTD (delivery at 34\u0026ndash;36 weeks), corresponding to a CL of 22 mm [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Therefore, the appropriate CL threshold in the third trimester for predicting PTD should probably be lower than 25 mm.\u003c/p\u003e \u003cp\u003eThe advantage of the present study lies in the comparative analysis of CL variations across the first, second and third trimesters and the association with PTD. Additionally, the large sample size employed in this study confers a degree of reliability to the findings. This study has several limitations. First, the number of women providing CL data from the first trimester was limited in scope. Second, this retrospective study analyzed CL measurements from the first, second and third trimesters separately. To augment the sample size, cases lacking CL data for a particular trimester were not excluded; thus, this study was not a continuous analysis of the same population. Consequently, the predictive contribution of CL measurements taken during the first, second and third trimesters to PTD, as well as the determination of the most appropriate threshold values, necessitates further investigation through prospective studies with larger sample populations.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eCL progressively decreases with increasing gestational age and has emerged as a more potent predictor of PTD after the 19th week of gestation. The defining threshold of a short cervix should probably be less than 25 mm at 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eCL \u0026nbsp; \u0026nbsp; \u0026nbsp;cervical length\u003c/p\u003e\n\u003cp\u003ePTD \u0026nbsp; \u0026nbsp; preterm delivery\u003c/p\u003e\n\u003cp\u003eROC \u0026nbsp; \u0026nbsp; receiver operating characteristic\u003c/p\u003e\n\u003cp\u003eAUC \u0026nbsp; \u0026nbsp; area under the curve\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by the Clinical Research Ethics Committee of Peking University First Hospital [No. 2023 (123-001)], and all participants signed informed written consent forms for their clinical records to be used in this study.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was supported by the National Key Research and Development Program (Grant No. 2022YFC2704605) to Yumei Wei.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was conceived and designed by Yumei Wei. The data was collected by Qidi Zhang, Xinyue Han and Yuchun Zhu with the support of Huixia Yang. The data was analyzed by Qidi Zhang, Xinyue Han and Yumei Wei. The paper was written by Qidi Zhang and Yumei Wei.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank the obstetricians involved in the project for collecting and analysing the data. And we appreciate all participating pregnant women for providing personal information.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eS. R. Walani. Global burden of preterm birth. Int J Gynaecol Obstet. 2020;150(1):31-33.\u003c/li\u003e\n\u003cli\u003eJ. Perin, A. Mulick, D. Yeung, F. Villavicencio, G. Lopez, K. L. Strong, D. Prieto-Merino, S. Cousens, R. E. Black and L. Liu. Global, regional, and national causes of under-5 mortality in 2000-19: an updated systematic analysis with implications for the Sustainable Development Goals. Lancet Child Adolesc Health. 2022;6(2):106-115.\u003c/li\u003e\n\u003cli\u003eW. H. Organization. WHO recommendations on interventions to improve preterm birth outcomes. 2015;\u003c/li\u003e\n\u003cli\u003eE. O. Ohuma, A. B. Moller, E. Bradley, S. Chakwera, L. Hussain-Alkhateeb, A. Lewin, Y. B. Okwaraji, W. R. Mahanani, E. W. Johansson, T. Lavin, et al. National, regional, and global estimates of preterm birth in 2020, with trends from 2010: a systematic analysis. Lancet. 2023;402(10409):1261-1271.\u003c/li\u003e\n\u003cli\u003eT. Wikstrom, H. Hagberg, B. Jacobsson, P. Kuusela, J. Wesstrom, P. Lindgren, H. Fadl, U. B. Wennerholm and L. Valentin. Effect of second-trimester sonographic cervical length on the risk of spontaneous preterm delivery in different risk groups: A prospective observational multicenter study. Acta Obstet Gynecol Scand. 2021;100(9):1644-1655.\u003c/li\u003e\n\u003cli\u003eQ. Feng, P. Chaemsaithong, H. Duan, X. Ju, K. Appiah, L. Shen, X. Wang, Y. Tai, T. Y. Leung and L. C. Poon. Screening for spontaneous preterm birth by cervical length and shear-wave elastography in the first trimester of pregnancy. Am J Obstet Gynecol. 2022;227(3):500 e1-500 e14.\u003c/li\u003e\n\u003cli\u003eI. Tsakiridis, T. Dagklis, A. Sotiriadis, A. Mamopoulos, L. Zepiridis and A. Athanasiadis. Third-trimester cervical length assessment for the prediction of spontaneous late preterm birth. J Matern Fetal Neonatal Med. 2023;36(1):2201368.\u003c/li\u003e\n\u003cli\u003eJ. D. Iams, R. L. Goldenberg, P. J. Meis, B. M. Mercer, A. Moawad, A. Das, E. Thom, D. McNellis, R. L. Copper, F. Johnson, et al. The Length of the Cervix and the Risk of Spontaneous Premature Delivery. New England Journal of Medicine. 1996;334(9):567-573.\u003c/li\u003e\n\u003cli\u003eJ. Visintine, V. Berghella, D. Henning and J. Baxter. Cervical length for prediction of preterm birth in women with multiple prior induced abortions. Ultrasound Obstet Gynecol. 2008;31(2):198-200.\u003c/li\u003e\n\u003cli\u003ePrediction and Prevention of Spontaneous Preterm Birth: ACOG Practice Bulletin, Number 234. Obstet Gynecol. 2021;138(2):e65-e90.\u003c/li\u003e\n\u003cli\u003eR. Maymon, M. Pekar-Zlotin, H. Meiri, Z. Haklai, E. S. Gordon, G. Shlichkov and H. Cuckle. Change in prevalence of preterm birth in Israel following publication of national guidelines recommending routine sonographic cervical-length measurement at 19-25 weeks\u0026apos; gestation. Ultrasound Obstet Gynecol. 2023;61(5):610-616.\u003c/li\u003e\n\u003cli\u003eC. B. Wulff, L. Rode, S. Rosthoj, E. Hoseth, O. B. Petersen and A. Tabor. Transvaginal sonographic cervical length in first and second trimesters in a low-risk population: a prospective study. Ultrasound Obstet Gynecol. 2018;51(5):604-613.\u003c/li\u003e\n\u003cli\u003eD. W. Gudicha, R. Romero, D. Kabiri, E. Hernandez-Andrade, P. Pacora, O. Erez, J. P. Kusanovic, E. Jung, C. Paredes, S. M. Berry, et al. Personalized assessment of cervical length improves prediction of spontaneous preterm birth: a standard and a percentile calculator. Am J Obstet Gynecol. 2021;224(3):288 e1-288 e17.\u003c/li\u003e\n\u003cli\u003eR. K. Ross, S. R. Cole, D. Westreich, J. K. Edwards, P. Musonda, B. Vwalika, M. P. Kasaro, J. T. Price and J. S. A. Stringer. Different effects for different questions: An illustration using short cervix and the risk of preterm birth. Int J Gynaecol Obstet. 2023;160(3):842-849.\u003c/li\u003e\n\u003cli\u003eP. Antsaklis, G. Daskalakis, A. Pilalis, N. Papantoniou, S. Mesogitis and A. Antsaklis. The role of cervical length measurement at 11-14 weeks for the prediction of preterm delivery. J Matern Fetal Neonatal Med. 2011;24(3):465-70.\u003c/li\u003e\n\u003cli\u003eE. Greco, A. Lange, F. Ushakov, J. R. Calvo and K. H. Nicolaides. Prediction of spontaneous preterm delivery from endocervical length at 11 to 13 weeks. Prenat Diagn. 2011;31(1):84-9.\u003c/li\u003e\n\u003cli\u003eA. P. Souka, I. Papastefanou, V. Michalitsi, K. Salambasis, C. Chrelias, G. Salamalekis and D. Kassanos. Cervical length changes from the first to second trimester of pregnancy, and prediction of preterm birth by first-trimester sonographic cervical measurement. J Ultrasound Med. 2011;30(7):997-1002.\u003c/li\u003e\n\u003cli\u003eE. Greco, R. Gupta, A. Syngelaki, L. C. Poon and K. H. Nicolaides. First-trimester screening for spontaneous preterm delivery with maternal characteristics and cervical length. Fetal Diagn Ther. 2012;31(3):154-61.\u003c/li\u003e\n\u003cli\u003eN. Sananes, N. Meyer, A. Gaudineau, G. Aissi, E. Boudier, G. Fritz, B. Viville, I. Nisand, B. Langer and R. Favre. Prediction of spontaneous preterm delivery in the first trimester of pregnancy. Eur J Obstet Gynecol Reprod Biol. 2013;171(1):18-22.\u003c/li\u003e\n\u003cli\u003eM. Parra-Cordero, A. Sep\u0026uacute;lveda-Mart\u0026iacute;nez, G. Rencoret, E. Vald\u0026eacute;s, D. Pedraza and H. Mu\u0026ntilde;oz. Is there a role for cervical assessment and uterine artery Doppler in the first trimester of pregnancy as a screening test for spontaneous preterm delivery? Ultrasound Obstet Gynecol. 2014;43(3):291-6.\u003c/li\u003e\n\u003cli\u003eO. Weitzner, T. Biron-Shental, Y. Daykan, O. Ezra and O. Markovitch. Can sonographic measurements and changes in cervical length during pregnancy predict preterm labour in an asymptomatic low-risk population? J Matern Fetal Neonatal Med. 2019;32(13):2107-2112.\u003c/li\u003e\n\u003cli\u003eA. Figarella, C. Chau, A. Loundou, C. d\u0026apos;Ercole and F. Bretelle. The introduction of a universal transvaginal cervical length screening program is associated with a reduced preterm birth rate. Am J Obstet Gynecol. 2023;228(2):219.e1-219.e14.\u003c/li\u003e\n\u003cli\u003eS. Parry, H. Simhan, M. Elovitz and J. Iams. Universal maternal cervical length screening during the second trimester: pros and cons of a strategy to identify women at risk of spontaneous preterm delivery. Am J Obstet Gynecol. 2012;207(2):101-6.\u003c/li\u003e\n\u003cli\u003eA. P. Souka, I. Papastefanou, A. Pilalis, D. Kassanos and G. Papadopoulos. Implementation of universal screening for preterm delivery by mid-trimester cervical-length measurement. Ultrasound Obstet Gynecol. 2019;53(3):396-401.\u003c/li\u003e\n\u003cli\u003eE. Hernandez-Andrade, E. S. Huntley, B. Sibai, S. C. Blackwell and E. E. Soto-Torres. A reduction in cervical length after starting vaginal progesterone in women with short cervix is significantly associated with preterm delivery \u0026lt;/=34 weeks and \u0026lt;37 weeks of gestation. Ultrasound Obstet Gynecol. 2023;\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Cervical Length, Pregnancy, Preterm Birth, Preterm Delivery, Risk Factors, Ultrasonography","lastPublishedDoi":"10.21203/rs.3.rs-4005959/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4005959/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eTo investigate the variations in cervical length (CL) across the first, second and third trimesters and the association with preterm delivery (PTD).\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eIn total, 16,352 women (32,543 measurements) who delivered singleton live births between January 1, 2020, and October 31, 2023, at Peking University First Hospitals were included in the present study. The associations between CL at three gestational weeks (9\u0026ndash;13\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e, 19\u0026ndash;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e and 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks) and PTD were evaluated using receiver operating characteristic (ROC) curves and logistic regression analysis. The chi-square test was used for comparisons of the incidence of PTD at or below each percentile for CL with patients with CL above the 75th percentile.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eWith increasing gestational age, there was a downward trend in CL at each percentile, with particularly obvious decreases in the 10th (31.5 mm and 27.1 mm), 5th (30.0 mm and 23.4 mm) and 1st (25.2 mm and 15.5 mm) percentiles after the 19th week of gestation. As gestational age increased, the predictive value of CL for PTD\u0026thinsp;\u0026le;\u0026thinsp;34\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks and PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks increased. After the 19th week of gestation, CL and PTD risk were negatively correlated when CL was less than or equal to the 75th percentile (all P\u0026thinsp;\u0026lt;\u0026thinsp;0.01). The incidence of PTD\u0026thinsp;\u0026lt;\u0026thinsp;37 gestational weeks was significantly higher among women with CL\u0026thinsp;\u0026le;\u0026thinsp;22.3 mm at 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks than among women with CL\u0026thinsp;\u0026le;\u0026thinsp;25 mm.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eCL progressively decreases with increasing gestational age and has emerged as a more potent predictor of PTD after the 19th week of gestation. The defining threshold of a short cervix should probably be less than 25 mm at 29\u0026ndash;33\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e gestational weeks.\u003c/p\u003e","manuscriptTitle":"Alteration and Predictive Ability of Cervical Length for Preterm Delivery in Each Gestational Trimester","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-12 17:31:59","doi":"10.21203/rs.3.rs-4005959/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"36a7eceb-ed5a-4d4d-a91e-585a58d36791","owner":[],"postedDate":"March 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-03-05T05:08:59+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-12 17:31:59","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4005959","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4005959","identity":"rs-4005959","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}