Association Between Intrapartum Papaverine Administration and the Risk of Obstetric Anal Sphincter Injuries: A Retrospective Cohort Study

INTRODUCTION AND HYPOTHESIS: Perineal trauma during vaginal delivery may result in long-term morbidity. We aimed to test the hypothesis that intrapartum administration of papaverine is associated with a lower incidence of obstetric anal sphincter injuries (OASIS) among primiparous patients. METHODS: This retrospective cohort study included primiparous patients with singleton term (> 37 weeks) pregnancies who delivered vaginally at Galilee Medical Center, Nahariya, Israel, between March 2020 and June 2024. Patients who received intrapartum 80 mg intramuscular papaverine were compared with those who did not. The primary outcome was the incidence of OASIS, defined as third- (3A, 3B, 3C) and fourth-degree perineal tears. Secondary outcomes included the incidence of first- and second-degree perineal tears and episiotomy. Multivariable logistic regression identified independent predictors of OASIS. RESULTS: Among 4939 patients, 1082 (21.9%) received papaverine. Baseline demographics of the two groups were comparable; however, patients who received papaverine had a higher BMI and a higher rate of labor induction. The incidence of OASIS was significantly lower in the papaverine group (0.5% vs 1.3%; adjusted absolute risk difference [aRD] -0.7%, 95% CI -1.2 to -0.1; p = 0.016). First- and second-degree perineal tears were less frequent in univariate analysis (35.2% vs 39.2%, p = 0.019); however, after multivariable adjustment, this association was attenuated and no longer statistically significant (aRD -1.3%, 95% CI -4.1 to 1.5; p = 0.37). Episiotomy rates of the two groups were comparable. CONCLUSIONS: In this study, primiparous patients who received intrapartum papaverine experienced a lower incidence of OASIS than those who did not receive papaverine. Further prospective, protocolized studies are needed to confirm these findings.