[Changes in the rates of preterm birth and multiparity over a 10-year period and multiparity as a possible risk factor for preterm birth].

Objective: To analyze the changes of preterm birth rate and proportion of multipara in 10 years, and to explore the possibility of multipara as a risk factor for preterm birth. Methods: This study was a cohort study. The general clinical data and pregnancy outcomes of 53 979 parturients delivered in Peking University First Hospital from January 2013 to December 2022 were collected, and the changes of preterm birth rate and proportion of multipara in the past 10 years were analyzed retrospectively. Single factor and multivariate logistic regression analysis were used to explore the risk factors of spontaneous preterm birth and the influence of multipara on pregnancy outcome. Results: (1) The total preterm birth rate of 53 979 parturients was 8.3%(4 478/53 979), and the overall preterm birth rate showed an upward trend in the past 10 years, among which the preterm birth rate was higher in 2017 and 2018, which were 8.9% and 9.2% respectively. The proportion of multipara was 24.9% (13 440/53 979), which showed a trend of rising first, then declining and then stabilizing. In 2017 and 2018, the proportion of multipara was the highest, accounting for 35.0%. (2) Multivariate logistic regression analysis showed that multipara was a risk factor for spontaneous preterm birth before 37 weeks of pregnancy (OR=1.678, 95%CI: 1.523-1.850; P<0.001), which was also a risk factor for spontaneous preterm birth before 34 weeks of pregnancy (OR=1.937, 95%CI: 1.632-2.301; P<0.001). The high risk factors of spontaneous preterm birth also include multiple pregnancies, hyperglycemia during pregnancy, abnormal amniotic fluid volume, premature rupture of membranes, intrauterine infection, cervical incompetence, history of cervical surgery and abnormal uterine development. (3) Compared with primiparas, multiparas was older, had earlier delivery weeks, higher premature delivery rate, higher birth weight and fewer multiple pregnancies. Among pregnancy complications, the incidence of gestational diabetes mellitus, placenta previa, placenta implantation, urgent delivery and macrosomia was higher, while the incidence of pregnancy-induced hypertension, pre-eclampsia, intrahepatic cholestasis of pregnancy, oligohydramnios, fetal growth restriction, premature rupture of membranes, intrauterine infection and postpartum hemorrhage was lower, and the differences were statistically significant (P<0.05). Conclusions: In recent 10 years, the overall rate of preterm birth is on the rise, and the risk factors of preterm birth are basically similar to those in previous studies. Multipara is a high-risk group of spontaneous preterm birth, and the risk of various pregnancy complications increases, which should be paid attention to in pregnancy care.