Risk of Obstetric Anal Sphincter Injuries after Labor Induction

Background: Obstetric Anal Sphincter Injuries (OASI) are associated with significant morbidity. Data regarding induction of labor (IOL) and risk of OASI is conflicting. The objective of this study is to evaluate if IOL increases the odds of OASI when compared to spontaneous labor. Methods: This is a retrospective case-control study in women with term, singleton pregnancies, who had a vaginal delivery at a single, academic center in an urban setting from October 2015 to December 2021. Individuals with the primary outcome, OASI, were identified and matched with controls (no OASI) by delivery date. Results: 303 OASI individuals were identified and matched with 1106 controls. Women with OASI were more likely to be White or Asian, have commercial insurance, and have a previous cesarean delivery (CD). IOL increased the likelihood of OASI by 49% compared to spontaneous labor (OR 1.49, 95% CI [1.138, 1.949]). IOL was no longer significant when adjusting for confounding variables and known risk factors. Conclusion: IOL was not associated with OASI when accounting for known antepartum and intrapartum risk factors. Further investigation of modifiable and non-modifiable risks during labor is imperative to decrease the risk of OASI and associated pelvic floor disorders.