Attempting vaginal birth after cesarean section (VBAC) places women at an increased risk for complications. We set out to identify factors that are predictive of major morbidity in women who attempt VBAC. A nested case-control study was performed within a large retrospective cohort study of women with a history of at least one cesarean. Women who attempted VBAC were identified and those who experienced at least one complication of a composite adverse outcome consisting of uterine rupture, bladder injury, and bowel injury (cases) were compared with those who did not experience one of these adverse outcomes (controls). We analyzed risk factors for major maternal morbidity using univariable and multivariable methods. The accuracy of the multivariable prediction model was assessed with receiver operator characteristic (ROC) curve analysis. Of 25,005 women with a history of previous cesarean, 13,706 (54.9%) attempted VBAC. The composite outcome occurred in 300 (2.1%) women attempting VBAC. Using logistic regression analysis, prior abdominal surgery (odds ratio [OR] 1.58, 95% confidence interval [CI] 1.2 to 2.1), augmented labor (OR 1.78, 95% CI 1.29 to 2.46), and induction of labor (OR 2.03, 95% CI 1.48 to 2.76) were associated with an increased risk of the composite outcome. Prior vaginal delivery (OR 0.39, 95% CI 0.29 to 0.54) was associated with decreased risk for the composite outcome. The ROC curve generated from the regression model has an area under the curve of 0.65 and an unfavorable tradeoff between sensitivity and specificity. Women attempting VBAC with a history of abdominal surgery or those who undergo augmentation or induction of labor are at an increased risk for major maternal morbidity, and women with a prior vaginal delivery have a decreased risk of major morbidity. The multivariable model developed cannot accurately predict major maternal morbidity.
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