(335) Effect of pre-pregnancy BMI vs. total pregnancy weight gain on trial of labor after cesarean

Thursday, January 30, 2025

10:30 AM – 12:30 PM

Coauthor(s)

LM

Logan McClure, MD

Resident physician
University of Tennessee Health Science Center
Memphis, Tennessee, United States

Submitting Author and Presenting Author(s)

Riley Short, MD

Resident physician
University of Tennessee Health Science Center
Memphis, Tennessee, United States

Coauthor(s)

PG

Patricia Goedecke, MS

Statistician
University of Tennessee Health Science Center
Memphis, Tennessee, United States
AS

Alexa Swailes, MD

Associate Program Director
University of Tennessee Health Science Center
Memphis, Tennessee, United States

Objective:
To examine whether pre-pregnancy BMI or total pregnancy weight gain is more closely associated with successful vaginal birth after Cesarean delivery (VBAC) in patients with term gestations with no prior history of vaginal delivery.

Study Design:
IRB approval was obtained for the study (24-09915-NHSR). The CDC National Center for Health Statistics birth certificate database was utilized to obtain relevant birth information from 2016-2022 in the United States. Inclusion criteria were term, singleton gestations in patients who underwent TOLAC with the following characteristics: second pregnancy with history of one prior Cesarean delivery, BMI >/= 18.5, and no pre-existing diagnosis of hypertensive disorders (either pre-gestational or gestational). Odds ratios and confidence intervals indicating likelihood of successful VBAC were developed both by (1) pre-pregnancy BMI alone, (2) total pregnancy weight gain alone, and (3) pre-pregnancy BMI stratified by total pregnancy weight gain.

Results:
12,164 patients met inclusion criteria for analysis, of whom 11,919 had data reported for both BMI and weight gain. Of these, 6,096 (51.1%) experienced a successful VBAC and 5,823 (48.9%) were delivered via repeat Cesarean section after TOLAC. Increasing pre-pregnancy BMI was associated with a lower likelihood of successful VBAC when compared to patients with a normal BMI (BMI 25-29.9: OR 0.75 [0.691, 0.825] vs. BMI 30-34.9: 0.56 [0.506, 0.624] vs. BMI 35.0-39.9: 0.56 [0.492, 0.645] vs. BMI >40: 0.36 [0.311, 0.433]) (All p values < 0.001). Among individuals with obesity, increased total pregnancy weight gain was significantly associated with decreased likelihood of VBAC success for those gaining greater than 20 pounds (21-30lbs: OR 0.76 [0.633, 0.909]; >30lbs: 0.75 [0.626, 0.887], p values < 0.001). However, when stratified by total pregnancy weight gain within each BMI category, no consistent significant differences in VBAC success were observed.

Conclusion: Our data suggest that pre-pregnancy BMI is more closely associated with likelihood of successful VBAC than total pregnancy weight gain within each BMI category.