Effect of body mass index and excessive weight gain on success of vaginal birth after cesarean delivery

OBJECTIVE: To estimate whether excessive weight gain or obesity are risk factors affecting success for vaginal birth after cesarean (VBAC). METHODS: Patients attempting VBAC were identified by the International Classification of Diseases, 9th Revision, codes "VBAC" and "non-primary C-section" and by reviewing logbooks on labor and delivery. A chart review identified patients attempting VBAC who were eligible for inclusion. Exclusion criteria included multiple gestation, more than one previous cesarean delivery, previous classical uterine scar, delivery at less than 36 weeks of gestation, and incomplete information. Patients were divided into the following categories: underweight (body mass index [BMI] < 19.8), normal weight (BMI 19.8-26), overweight (BMI 26.1-29), and obese (BMI > 29). Excessive weight gain was defined as a weight gain of, more than 40 lb. Variables of interest included diabetes, previous successful vaginal delivery or VBAC, and presence of recurrent indication for cesarean delivery. RESULTS: We identified 1,213 patients who met inclusion criteria. Overall, the VBAC success rate was 77.2%. The success rates for BMI less than 19.8, 19.8-26, 26.1-29, and greater than 29 were 83.1%, 79.9%, 69.3%, and 68.2%, respectively, P < .001. Obese patients were almost 50% less likely to have a successful VBAC when compared to underweight patients, odds ratio 0.53, 95% confidence interval 0.29-0.98, P = .043. Similarly, patients who gained more than 40 lb were almost 40% less likely to be successful at VBAC than those who gained less than that amount, odds ratio 0.63, 95% confidence interval 0.42-0.97, P = .034. They had a VBAC success rate of 66.8%, whereas patients who gained less than 40 lb were successful 79.1% of the time, P < .001. CONCLUSION: Excessive weight gain during pregnancy and obesity both decrease VBAC success. Proper patient selection will help increase the likelihood of successful VBAC.