The risk factors and causes of spontaneous preterm birth in women with previous term delivery

Abstract

Previous spontaneous preterm delivery is the most important risk factor of preterm birth, whereas term delivery without obstetric complication is a reassuring evidence for the subsequent pregnancy. However, we sometimes experience spontaneous preterm birth after uncomplicated term delivery. This study was performed to evaluate the risk factors and causes of spontaneous preterm birth after previous term delivery(sPAT). Retrospective cohort study was performed. Singleton pregnant women with spontaneous preterm birth whose previous pregnancy outcomes had been uncomplicated term deliveries were enrolled. We analyzed their causes of preterm birth and compared clinical characteristics and perinatal outcomes to controls with two consecutive term deliveries during the same period. The optimal interpregnancy interval(OPI) was defined between 18-59 months. Preterm birth with maternal-fetal indication, stillbirth, or congenital anomaly were excluded. A total 196 pregnant women met the inclusion criteria and 463 women were selected as controls. The mean gestational age at delivery was 33+3 weeks of gestation in sPAT group. Preterm premature rupture of membrane(PPROM) was the most common cause of spontaneous preterm birth, followed by preterm labor with intact membrane, and cervical insufficiency. The cervical lengths at midtrimester in the sPAT group were above 2.5cm in most cases. Women with sPAT had less total weight gain and average weight gain per week during pregnancy compared to controls. The proportion of women with OPI was significantly lower in women with sPAT than in controls. The cesarean delivery(CD) rate of the index term pregnancy was similar between the two groups, but the CD rate of the subsequent pregnancy was significantly higher in sPAT group than controls. Unlike the general spontaneous preterm birth, PPROM is the cause of preterm birth in more than half of the women with sPAT. Lower weight gain during pregnancy and inadequate interpregnancy interval were associated with preterm birth even in women with a previous term delivery.