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

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

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

Study Design: 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).

Results: 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).

Conclusions: 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.