ABSTRACT
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%CI2.265-3.643), 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.