Factors for successful vaginal delivery in twin pregnancies: a ten-year single-center retrospective study.

BACKGROUND: When certain conditions are met, a large randomized trial has suggested that for twin pregnancies, vaginal delivery does not increase adverse maternal or neonatal outcomes compared with cesarean section. However, the choice of the delivery mode is sometimes controversial, and policies can vary across different facilities. Identifying factors associated with successful vaginal delivery is important in reducing unnecessary cesarean sections. METHODS: We retrospectively analyzed 370 twin pregnancies delivered after 32 weeks of gestation at our hospital between April 2012 and March 2022, excluding monoamniotic monochorionic twins. Vaginal delivery was offered when the first twin was in cephalic presentation, the estimated fetal weight of each twin was at least 1500 g, and there were no other indications for cesarean section. We compared maternal and fetal factors between successful and failed attempts at vaginal delivery. Notably, we used multivariable logistic regression and the classification and regression tree (CART) method for statistical analyses. RESULTS: Of the 370 twin pregnancies, 133 women attempted vaginal delivery, and 115 (86.5%) achieved successful vaginal delivery of both twins. Multivariable analysis identified multiparity (adjusted odds ratio 15.29, 95% confidence interval 3.55-65.74; p < 0.001) and younger maternal age (adjusted odds ratio 0.84 per year, 95% confidence interval 0.73-0.96; p = 0.013) as independent predictors of successful vaginal delivery. CART analysis supported these findings, identifying parity as the primary discriminator. Among primiparas, maternal age ≤ 29 years emerged as a cutoff, with younger women having a higher probability of successful vaginal delivery. Univariable comparisons further supported this result. CONCLUSIONS: Our findings suggest that multiparous women, regardless of maternal age, and primiparous women aged ≤ 29 years are associated with a high probability of successful vaginal twin delivery.