Prediction of successful trial of labor after cesarean - the benefit of prior vaginal delivery

Objective: To determine predictive factors for vaginal birth after cesarean section (VBAC). Methods: A retrospective cohort study of all women with singleton pregnancies and a prior single low transverse cesarean section (CS) who attempted vaginal delivery in a tertiary hospital (2010-2014). Pregnancy outcome of women with VBAC was compared to those who failed vaginal delivery. Sub-analysis for women with no prior vaginal deliveries was performed. Pregnancies with non-cephalic presentation, estimated fetal weight>4000 g and any contraindications for vaginal delivery were excluded. Results: Of the 40 714 deliveries, 1767 women met inclusion criteria. Among them 1563 (88.5%) had a VBAC and 204 (11.5%) failed. There was no significant difference between the groups regarding maternal age, comorbidities and pregnancy complications. Predictors for VBAC were (odds ratio, 95% confidence interval) interval from prior CS (1.13, 1.04-1.22, p = 0.004), previous VBAC (2.77, 1.60-4.78, p<0.001), prior vaginal delivery prior to the CS (3.05, 1.73-5.39, p<0.001) and induction of labor (0.62, 0.40-0.97, p = 0.03). For women with no prior vaginal birth, only birthweight was associated with VBAC (0.99, 0.99-1.00, p = 0.02). Conclusion: While different variables may influence the rate of VBAC, the predictive ability of VBAC for women with no previous vaginal deliveries remains poor.