Prevalence of preterm birth and risk factors associated with it at different gestational ages: A multicenter retrospective survey in China.

Objectives: To investigate the prevalence of preterm birth (PTB) and the risk factors for different gestational age subgroups of preterm birth in China.

Methods: We carried out a descriptive cross-sectional study encompassing all singleton live births (24 to 41 weeks) with completed data in 23 provinces in China from 2010 to 2017 during investigation period. We compared both the preterm group (24 to 36 weeks) and preterm subgroups (<32 weeks, 32 to 33 weeks, and 34 t0 36 weeks) with the term group (37 to 41 weeks). We collected information on maternal and fetal characteristics from medical records. Logistic regression was use.

Results: The prevalence of PTB was 7.4% (15,833/215,254) in singleton births. After adjusting for maternal age, parity, and potential risk factors in univariate analysis, the high-risk factors for PTB at <32 weeks were placental abruption (aOR=41.52; 95% CI, 25.89-66.58), placenta previa (aOR=40.04; 95% CI, 32.00-50.09), chorioamnionitis (aOR=11.06; 95% CI, 8.738-14.02), and hypertension disorders in pregnancy (HDP) (aOR=3.564; 95% CI, 2.930-4.335). Intrahepatic cholestasis of pregnancy (ICP) was significantly associated with PTB at 34-36 weeks (aOR=5.763; 95% CI, 5.049-6.577), particularly with spontaneous PTB (aOR=10.04; 95% CI, 8.79-11.47). Gestational diabetes mellitus (GDM) was significantly associated with PTB at 34-36 weeks only (aOR=1.156; 95% CI, 1.054-1.267).

Conclusion: Placental abruption, placenta previa, chorioamnionitis, and HDP were more predictive of early PTB; GDM and ICP were more predictive of late PTB.