OP11 .05: Induction of labor in preterm pregnancies compared with term pregnancies

To estimate the likelihood of Cesarean delivery in preterm pregnancies (< 37 weeks of gestation) undergoing labor induction as compared with term pregnancies. This is a matched case–control study of 172 preterm women and 344 women at term, as control, undergoing induction of labor between 2004 and 2012. Cases and controls were matched on the parity, maternal weight, maternal height and age. Ultrasound measurement of the cervical length and determination of the Bishop score were performed before induction of labor. The data on potential confounders, including maternal characteristics and clinical and ultrasound parameters, were collected from both groups. The primary outcome was mode of delivery. Cesarean delivery was significantly higher in the group with preterm pregnancies (26.2% versus 12.4%, P < 0.001). However, as expected, the preterm pregnant women had a significantly higher mean cervical length and lower median Bishop score, and were more likely to have higher ratio of maternal to fetal indications for labor induction, as compared with term pregnant women. On adjusted analysis of risk factors for Cesarean delivery in women undergoing induction, preterm pregnancy was not independently associated with Cesarean delivery after controlling for indications of induction, cervical length, Bishop score, use of ripening agents, age, weight, height, parity, and epidural analgesia. In preterm gestations, logistic regression analysis identified parity and gestational age at the time of induction, but not cervical length or Bishop score, as the best predictors of Cesarean delivery. Although the risk of Cesarean delivery is significantly increased in women with preterm pregnancies undergoing labor induction compared with term pregnancies undergoing induction of labor, preterm pregnancy is not an independent factor for Cesarean delivery. The majority of preterm pregnant women undergoing induction still had successful vaginal deliveries.