Risk factors of unsuccessful vaginal twin delivery

Twin trial of labor presents a challenge to obstetricians, as it is associated with a greater number of adverse birth outcomes compared with singleton deliveries. The risk of poor outcome has shown to be highest with unsuccessful vaginal twin delivery. The purpose of this study was to identify the clinical risk factors associated with intrapartum cesarean section in late preterm and term twin births.

All live diamniotic twin deliveries of at least 35⁺⁰ weeks of gestation with planned vaginal delivery were included in this retrospective single-center cohort study. Maternal and newborn characteristics were compared between a vaginal delivery group and an intrapartum cesarean section group. Logistic regression analysis was carried out to determine independent risk factors of intrapartum cesarean section. Further, maternal and neonatal outcomes were compared between groups of vaginal delivery and cesarean section for both twins and also between groups of vaginal delivery and cesarean section for the second twin only (combined delivery). The impact of presentation of the second twin on the mode of twin delivery and on neonatal outcome was also examined.

Among 821 twin pregnancies, 581 mothers (70.8%) attempted trial of labor and were eligible for the study. With a cephalic-presenting first twin, the trial of labor rate was 89.3% and vaginal delivery was successful in 82.8%. Nulliparity (odds ratio [OR] 3.2, 95% confidence interval [CI] 2.0-5.1) and non-cephalic presentation of the second twin (OR 3.0, 95% CI 1.9-4.8) were found to be independent risk factors of cesarean section. However, 76.1% of mothers with non-cephalic second twins achieved vaginal delivery and perinatal outcomes were comparable with cases of cephalic-presenting second twins. When comparing delivery modes, maternal outcomes were more favorable with vaginal delivery, whereas combined delivery increased the second twin's risk of adverse neonatal outcome.

This study, with high rates of trial of labor and successful vaginal twin delivery, found nulliparity and non-cephalic presentation of the second twin to be risk factors of intrapartum cesarean section in twin pregnancies.