The impact of perineal warm compress implementation on obstetric anal sphincter injury: initial evaluation of a quality improvement project

Background Obstetric anal sphincter injury (OASI) is a severe complication of vaginal birth. Perineal warm compress during the second stage of labor has been shown to decrease the rate of OASI in randomized controlled trials. Objectives This retrospective study evaluated the outcomes of a Quality Improvement (QI) project whose aim was to increase the use of warm compress on a labor and delivery unit at a tertiary-care center. Study Design We included all vaginal births ≥24+0 weeks' gestation occurring on the labor and delivery unit in the thirteen months before (June 2023 to June 2024) and after initiation of a QI project (July 2024 to July 2025). The primary outcomes were warm compress use and the OASI rate. A run chart was utilized to plot the monthly use of warm compress. The OASI proportion was compared before and after the QI project using a chi-squared test. The impact of warm compress exposure with covariate adjustment, either before or during the QI project, was evaluated using inverse probability of treatment weighting. Relative risk (RR) of OASI with 95%CI and p-values were reported. The analysis was repeated for a high risk subgroup: primiparous births occurring at term. Results 8415 vaginal births were included: 4272 before and 4143 during the QI project. Covariates were similar between the two periods. 4299 (51%) of births were among primiparous participants delivering at term. Warm compress documentation increased during the project (mean: 17.9% vs. 45.6%); however, there was consistent rise in the year prior to project start. Warm compress use was higher among term primiparous births throughout the study. OASI proportion was lower during the QI project, but this was not statistically significant (all vaginal births: 4.6% vs. 4.0%, p=.2; term primiparous births: 7.8% vs. 6.3%, p=.06). After Adjusting for covariates, warm compress exposure was associated with a lower risk of OASI among term primiparous births (aRR=0.77, 95% CI 0.59 to 0.99, p=.04), but not all vaginal births (aRR=0.88, 95% CI 0.70 to 1.10, p=.26). Conclusion Initial implementation of perineal warm compress did not significantly reduce the rate of OASI. Adjusted analysis showed that warm compress exposure modestly reduced the risk of OASI among first vaginal births at term, but not all vaginal births.