Disparities in Planned and Successful Vaginal Delivery after a Cesarean Delivery by Body Mass Index: a Population-Based Cohort Study

Background: Previous literature suggests that pregnant individuals with obesity have fewer planned and successful vaginal births following a previous cesarean delivery. Concern is growing that discrimination based on body mass index (BMI) and comorbidities associated with BMI, rather than BMI itself, are primarily responsible for these findings. Objective: To describe disparities in planning and having a successful vaginal delivery after a previous cesarean delivery by BMI status. Study Design: This population-based cohort study included all singleton pregnancies ≥37 weeks’ gestation from 2003 to 2021 in Nova Scotia, Canada, with one previous cesarean and without contraindications for a trial of labor. Adjusted risk ratios (aRRs) and 95% confidence intervals (CIs) were estimated using Poisson regression, incorporating inverse probability weighting to account for confounding by demographic characteristics and co-morbidities. Results: Among 12 646 deliveries, approximately 31% experienced pre-pregnancy obesity. Of those with obesity, 34% planned a vaginal birth compared to 44% of those without obesity (aRR: 0.82, 95% CI: 0.78, 0.86). Higher BMI classification was associated with a reduced likelihood of planned vaginal delivery: class I: 37%, aRR: 0.88 (95% CI: 0.82, 0.94); class II: 32%, aRR: 0.81 (95% CI: 0.74, 0.89); class III: 26%, aRR 0.65 (95% CI: 0.56, 0.75). Among those planning a vaginal delivery, those with obesity were less likely to have a vaginal birth compared to those without obesity (57% vs 69%; aRR: 0.87, 95% CI: 0.82, 0.92); successful vaginal birth was less likely as BMI increased. Conclusion: Obesity was associated with reduced planned and successful vaginal delivery after a previous cesarean delivery and the association was most pronounced at higher BMI after accounting for demographic characteristics and co-morbidities. While discrimination based on BMI was unmeasured, notable disparities in planning and having a vaginal delivery by BMI suggest that training for health care providers and the availability of appropriate infrastructure may help optimize care for this population.