788: Is induction with early amniotomy associated with a higher likelihood of vaginal birth after cesarean?

Abstract

The cesarean section (CS) rate are increasing. In an attempt to reduce CS rates, a mighty effort is being made to offer eligible women the opportunity to attempt vaginal birth after cesarean (VBAC). We sought to evaluate the impact of early amniotomy on VBAC success. Case-control study using MFMU Cesarean Registry. Women included had singleton pregnancy, prior cesarean attempting VBAC, and induction of labor with amniotomy (AROM). Cases were defined as subjects with VBAC, controls with unsuccessful VBAC (nVBAC). Early AROM defined as amniotomy at <4cm. We also assessed impact of amniotomy at <6cm given new labor curves (AROM<6). Demographic and obstetric characteristics were compared using Student’s T-test, Fisher’s exact, and Wilcoxon rank-sum as appropriate. Multivariate logistic regression performed to control for confounding. Of the 1490 women included, 1134 (767.11%) had VBAC. VBAC women were more likely to have a lower BMI, prior vaginal delivery, be augmented with Pitocin and have prenatal care (Table 1). nVBAC women were more likely to be African American, on Medicaid, have obstetric complications and be induced at >40 weeks (Table 1). VBAC women had early AROM 59.5% of the time vs 63.2% in nVBAC (p=0.24). AROM<6 also did not differ (91.2% vs 89.3%, p=0.30). When controlling for confounders, early amniotomy was associated with a 34% reduction in likelihood of VBAC (p<0.01). AROM<6 was not associated with increased odds of nVBAC (AOR 0.93, 95% CI 0.57- 1.53). Of note, women who had early amniotomy did not have higher rates of chorioamnionitis (2.8% vs 2.9%, p>0.99). In an effort to reduce the CS rate, understanding factors that impact success rate of VBAC is critical. Unlike data from nulliparous women, induction with early amniotomy does not appear to increase the likelihood of VBAC.