Obstetric Anal Sphincter Injury: Vaginal Birth After Cesarean Versus First Vaginal Delivery

Modern data regarding the relationship between vaginal birth after cesarean (VBAC) and obstetric anal sphincter injury (OASI) are minimal with mixed results.

The aim of the study was to determine if VBAC is associated with an increased risk of OASIs.

This was a retrospective cohort study of liveborn deliveries from 2018 to 2022 within a large, multihospital academic health system. The primary outcome was the proportion of OASIs compared between patients who underwent a first vaginal delivery (primiparous vaginal delivery group) versus patients who underwent a first VBAC (VBAC group).

A total of 17,044 patients were included. A total of 16,208 had a primiparous vaginal delivery and 836 underwent VBAC. Vaginal birth after cesarean patients were older (29.9 vs 27.0 years, P  < 0.01), more likely to self-identify as Black or Asian race (26.1% vs 18.0%, P  < 0.01), and had lower maternal weight (182.7 vs 187.2 lbs, P  < 0.01). The proportion of OASIs was significantly higher in the VBAC group (6.9% vs 5.1%, P  = 0.02). Vacuum-assisted vaginal deliveries were more common in the VBAC group (7.7% vs 5.4%, P  < 0.01).On multivariable logistic regression, VBAC was not significantly associated with OASIS (odds ratio [OR] = 1.01, 95% confidence interval [CI] = 0.75-1.36, P  = 0.95). Operative vaginal delivery (OR = 6.44, CI = 5.51-7.52, P  < 0.01), older maternal age (OR = 1.05, CI = 1.03-1.07), and Asian race (OR 2.62, CI = 2.10-3.26) demonstrated increased odds of OASIs. Patients who identified as Black demonstrated lower odds of OASIs (OR = 0.68, CI = 0.50-0.93).

While there was a greater proportion of OASIs in the VBAC group compared to the primiparous vaginal delivery group, VBAC was not an independent risk factor.