(919) The effect of pre-pregnancy and delivery BMI on TOLAC success in a high-risk cohort

Friday, January 31, 2025

10:30 AM – 12:30 PM

Submitting Author and Presenting Author(s)

Shannon R.O Moran, MD

Resident Physician
University at Buffalo
Buffalo, NY, United States

Coauthor(s)

JS

James A. Shelton, MS

Epidemiologist
University at Buffalo
Buffalo, New York, United States
Dawei David Wang, BS, MD

Fellow Physician
University at Buffalo
Buffalo, New York, United States

Objective: Rates of trial of labor after cesarean section (TOLAC) and obesity have increased in today’s population. Vaginal birth after cesarean section (VBAC) has been shown to reduce maternal morbidity. Published predictive models for VBAC success take into account both body mass index (BMI) and chronic hypertension. However, no previous studies have specifically analyzed the effect of BMI on TOLAC success in those with any form of hypertension. Therefore, we sought to investigate whether pre-pregnancy BMI or delivery BMI has a greater effect on TOLAC success rate in this high-risk cohort.

Study Design: This was a retrospective cohort study of national birth certificate data from 2022. We included all singleton, vertex livebirths with no fetal anomalies who had 1 prior cesarean delivery and a diagnosis of either chronic hypertension or a hypertensive disorder of pregnancy who attempted TOLAC. Those with prior vaginal deliveries were excluded. Patients were divided into 6 groups by pre-pregnancy and delivery BMI. Two logistic regression models, one for pre-pregnancy and one for delivery BMI, were created. These were compared using Akaike Information Criterion (AIC) and receiver operating characteristic (ROC) curves. Confounding variables included were maternal age and race, maternal weight gain, chronic and gestational diabetes, gestational age, birthweight, and induction of labor.

Results: 5,144 patients were included. 2,382 had a repeat cesarean section. 2,762 had a VBAC. For both pre-pregnancy and delivery BMI, the rate of VBAC decreased as obesity class increased. In the AIC analysis, pre-pregnancy BMI and delivery BMI produced almost identical results (6685 versus 6670, respectively). Furthermore, in the ROC curve, again pre-pregnancy BMI and delivery BMI produced almost identical results (0.631 versus 0.634, respectively).

Conclusion: Pre-pregnancy BMI and delivery BMI have similar effects on TOLAC success in those with hypertension of any form, with decreased rates of VBAC seen with increasing BMI. Both should be used to counsel patients on TOLAC in this high-risk cohort throughout the antepartum period.