Objective: To analyze the incidence of preterm birth based on pre-pregnancy body mass index (BMI) stratification and explore the associated factors of preterm birth among pregnant women at different BMI stratifications. Methods: From February 2018 to December 2020, pregnant women who participated in China Birth Cohort Study (CBCS) and gave birth at Beijing Obstetrics and Gynecology Hospital were enrolled as the study subjects. Electronic Data Capture System and standard structured questionnaires were used to collect data related to pre-pregnancy, pregnancy, and delivery for pregnant women. Pregnant women were divided into the low-weight group, normal-weight group and overweight group based on their pre-pregnancy BMI. A Cox proportional hazards model was used to analyze the associated factors of preterm birth among pregnant women with different BMI before pregnancy. Results: A total of 27 195 singleton pregnant women were included, with a preterm birth rate of 5.08% (1 381/27 195). The preterm birth rates in the low-weight group, normal-weight group and overweight group were 4.29% (138/3 219), 4.63% (852/18 390) and 7.00% (391/5 586) respectively (P<0.001). After adjusting for relevant factors, the Cox proportional hazards model showed that the risk of preterm birth in the overweight group was 1.457 times higher than that in the normal-weight group (95%CI: 1.292-1.643). Preeclampsia-eclampsia (HR=2.701, 95%CI: 1.318-5.537) was the associated factor for preterm birth in the low-weight group. Advanced maternal age (HR=1.232, 95%CI: 1.054-1.441), history of preterm birth (HR=4.647, 95%CI: 3.314-6.515), vaginal bleeding in early pregnancy (HR=1.613, 95%CI: 1.380-1.884), and preeclampsia-eclampsia (HR=3.553, 95%CI: 2.866-4.404) were associated factors for preterm birth in the normal-weight group. Advanced maternal age (HR=1.473, 95%CI: 1.193-1.818), history of preterm birth (HR=3.209, 95%CI: 1.960-5.253), vaginal bleeding in early pregnancy (HR=1.636, 95%CI: 1.301-2.058), preeclampsia-eclampsia (HR=2.873, 95%CI:2.265-3.643), and pre-gestational diabetes mellitus (HR=1.867, 95%CI: 1.283-2.717) were associated factors for preterm birth in the overweight group. Conclusion: Pre-pregnancy overweight is an associated factor for preterm birth, and there are significant differences in the associated factors of preterm birth among pregnant women with different BMI before pregnancy.
目的： 分析基于孕前体重指数（BMI）分层的早产发生率，探究各BMI层级孕妇发生早产的关联因素。 方法： 选择2018年2月至2020年12月在首都医科大学附属北京妇产医院进入“中国出生人口队列研究”的单胎妊娠孕妇为研究对象。采用电子数据采集系统及标准结构化问卷收集孕妇孕前、孕期及分娩相关数据。根据孕前BMI将孕妇分为偏瘦组、正常组及超重组，采用Cox比例风险回归模型，分析不同孕前BMI孕妇早产的关联因素。 结果： 共纳入27 195例单胎活产孕妇，其早产发生率为5.08%（1 381/27 195），偏瘦组、正常组及超重组的早产发生率分别为4.29%（138/3 219）、4.63%（852/18 390）和7.00%（391/5 586），差异有统计学意义（P<0.001）。调整相关因素后，Cox比例风险回归模型显示，孕前超重组孕妇早产发生的风险是正常体重组孕妇的1.457倍（95%CI：1.292~1.643）。子痫前期-子痫是孕前偏瘦孕妇早产发生的关联因素（HR=2.701，95%CI：1.318~5.537）；高龄（HR=1.232，95%CI：1.054~1.441）、早产史（HR=4.647，95%CI：3.314~6.515）、孕早期阴道出血（HR=1.613，95%CI：1.380~1.884）、子痫前期-子痫（HR=3.553，95%CI：2.866~4.404）是孕前体重正常孕妇早产发生的关联因素；高龄（HR=1.473，95%CI：1.193~1.818）、早产史（HR=3.209，95%CI：1.960~5.253）、孕早期阴道出血（HR=1.636，95%CI：1.301~2.058）、子痫前期-子痫（HR=2.873，95%CI：2.265~3.643）、孕前糖尿病（HR=1.867，95%CI：1.283~2.717）是孕前超重孕妇早产发生的关联因素。 结论： 孕前超重是早产的关联因素，孕前不同BMI孕妇发生早产的关联因素有差异。.