581: Does gestational weight gain affect TOLAC success?

Objective: The Institute of Medicine (IOM) recommends targets for gestational weight gain according to pre-pregnancy body mass index (BMI). Although maternal obesity reduces the likelihood of vaginal birth after cesarean (VBAC) success in published predictive models, the impact of gestational weight gain has not been described in relationship to IOM guidelines. We aimed to study VBAC success in women who met or exceeded IOM gestational weight gain recommendations. Study Design: This was a retrospective cohort study of all women attempting trial of labor after cesarean delivery (TOLAC) at an academic tertiary care institution from 2011-2018. Singleton, viable, nonanomalous pregnancies ≥ 37 weeks were included. Pre-pregnancy weight was defined as last measured weight in the 6 months preceding pregnancy or the earliest weight recorded in pregnancy before 14 weeks gestation. Delivery weight was recorded on admission for delivery. Women without a recorded pre-pregnancy or delivery weight were excluded. Gestational weight gain was the difference between delivery and pre-pregnancy weights. The cohort was analyzed according to VBAC success. BMI classes were compared according to whether they met or exceeded IOM gestational weight gain recommendations. Statistical analysis included chi-squared, Fisher’s exact test and Mann-Whitney U test. Results: Of 1,397 women undergoing TOLAC, 1,193 met study criteria. 877 (73%) had a successful VBAC (Table). Although pre-pregnancy BMI was higher in women with failed TOLAC (32 [26-39] kg/m2) than successful VBAC (29 [25-35] kg/m2, p < 0.001), gestational weight gain was similar in both groups (19 [6-30] vs 20 [9-33] lbs, p = .1). When VBAC success was evaluated according to BMI category, women who exceeded IOM guidelines for weight gain had lower VBAC rates (Figure). Women with gestational weight gain exceeding IOM guidelines had decreased odds of successful VBAC in BMI categories of BMI 25-29.9 (OR 0.54, 95% CI 0.32-0.92, p=.02) and BMI 35-39.9 (OR 0.49, 95% CI 0.25-0.95, p=.03). This difference was not significant for other BMI categories. Conclusion: Although increasing delivery BMI was associated with lower VBAC success, gestational weight gain was similar in failed TOLAC and successful VBAC. Exceeding IOM gestational weight gain recommendations predicted lower VBAC success for some but not all BMI categories. Further study is needed to characterize the relationship between VBAC success and gestational weight gain. [Figure presented] [Figure presented]