812: Vaginal birth after cesarean (VBAC) is associated with an increased risk for instrumental delivery

Abstract

Counseling patients regarding trial of labor after cesarean delivery (TOLAC) is a clinical challenge. While much attention is given to the adverse outcome associated with TOLAC failure, data regarding the rate of instrumental delivery in this population is sparse. We aimed to determine whether TOLAC is associated with an increased risk for instrumental delivery. A retrospective cohort study in a tertiary medical center included pregnant women at term who attempted first vaginal delivery. The participants were classified into: 1. Primiparous women attempting TOLAC (n=1747) and 2. nulliparous gravida (n=19,416). The rates of cesarean and instrumental delivery were compared. The rate of instrumental deliveries was higher in the TOLAC group compared to controls (17.3 vs. 15% respectively, p=0.01). When only women who had a successful vaginal delivery were compared, the difference in the rate of instrumental deliveries was more prominent (23.9 vs. 17.1% respectively, p<0.0001). This disparity remained significant even when only participants with a prior elective cesarean were included in the analysis (21.1 vs.17.1% respectively, p=0.004). After adjustment for maternal age, BMI, gestational age, birthweight and duration of second stage- VBAC was found to be independently associated with instrumental deliveries. Nearly one quarter of first successful VBAC will end by instrumental delivery. This may reflect lower tolerance for second stage abnormalities during TOLAC.