Low volume forceps practice and anal sphincter injury rate

Purpose: While the increased rates of high degree perineal tears were previously associated with the use of forceps, in the current era of low volume of forceps practice, factors associated with the occurrence of this potential complication remain understudied. We aim to evaluate factors associated with obstetric anal sphincter injury (OASIS) in obstetric units with a low volume forceps practice. Methods: A retrospective cohort study was conducted at two tertiary medical centers. All singleton pregnancies delivered by forceps extraction between 2011 and 2019 were analyzed. Women who experienced anal sphincter injury were compared to those who did not. Results: The study cohort included 764 forceps deliveries. There were 19 (2.5%) cases of OASIS. Women with anal sphincter injury had higher rates of gestational diabetes mellitus (21% vs. 5.6%, OR [95% CI] 4.46 (1.41–14.04), p = 0.02). Birth weights and the rate of macrosomia did not differ between groups. Induction of labor was more common among the OASIS group (68% vs. 41.7%, OR [95% CI] 3.0 (1.1–8.0), p = 0.02). Sequential use of forceps (after failed vacuum attempt) was associated with OASIS (8 (42%) vs. 76 (10.2%), OR [95% CI] 6.4 (2.5–16.4), p < 0.001). In a multivariate logistic regression, sequential forceps was the only factor independently associated with OASIS (OR [95% CI] 4.7 (1.3–18.2), p = 0.02). Conclusions: Rate of OASIS was relatively low in the current cohort. Sequential use of forceps was found to be the most important determinant in OASIS occurrence.