810: Can we improve our ability to predict VBAC success in the contemporary labor management era

Abstract

The Maternal Fetal Medicine-Units Network (MFMU) antenatal vaginal birth after cesarean (VBAC) prediction model has been used to aid clinicians in counseling patients but labor management has changed since its development. Secondary to the model’s suboptimal performance in our population, we aimed to identify factors predictive of success in the contemporary era of labor management. This is a retrospective cohort study of all women with one prior low transverse cesarean who underwent a trial of labor (TOLAC) at term with a non-anomalous singleton gestation between January 2011 and May 2018 at out academic tertiary care center. Regression analysis incorporated clinical factors available early in pregnancy. Data regarding antepartum factors that may influence TOLAC success and maternal and neonatal outcomes was also extracted from medical records for evaluation (Table 1). A receiver operating characteristic curve for our model was compared to the MFMU model to compare their performance. Of 1307 VBAC attempts, 1042 pregnancies met inclusion criteria with all of the variables necessary for calculation of predicted VBAC success using the MFMU model. The derived model includes seven antenatal factors: age, race, height, intake weight, number of prior vaginal deliveries, pregestational diabetes, and history of tobacco use (Table 2). The median predicted VBAC success rate was 76.6 % (IQR 64.8, 86.3) while the observed success rate was 74.2 % (difference 2.4 %, 95% CI -1.3-6.1 %). The median predicted probability of success was significantly higher for women who had a successful TOLAC (median 79.6 % (IQR 68.6, 88.1) than for those who had a repeat cesarean (66.1 % (IQR 54.8, 77.9, P < .0001). Area under the curve (AUC) for the model is 0.72 (95% confidence interval (CI) 0.68-0.75) which indicates better performance compared to the MFMU antenatal model which had a AUC of 0.69 (95% CI 0.65 – 0.72, P <.01). VBAC success is correlated with seven readily attainable antenatal clinical factors that, along with the predictive model that incorporates them warrant further investigation as they may improve our ability to predict VBAC success and counseling in the contemporary era of labor management.