Defining an at-risk population for obstetric anal sphincter laceration.

Objective: The purpose of this study was to calculate the number of cesarean deliveries needed to prevent 1 case of obstetric anal sphincter laceration associated with operative vaginal delivery in an at-risk cohort.

Study Design: An institutional, computerized database was used to analyze women with obstructed labor who could have been managed by either operative vaginal or cesarean delivery from September 2006 to March 2008. Women with 1 or more of the following diagnoses comprised the cohort: cephalopelvic disproportion (CPD), arrest of descent, maternal exhaustion, and fetal distress.

Results: Fifty (23.9%) out of a total of 209 women managed by operative vaginal delivery experienced an anal sphincter laceration compared to none of 254 women in the cesarean delivery group (P < .0001). The ARR therefore was 23.9% (95% confidence interval, 18.1-29.7) and the NNT was 4.2 (95% confidence interval, 3.4-5.5).

Conclusion: Five cesarean deliveries are needed to prevent 1 anal sphincter laceration associated with operative vaginal delivery in this cohort.