Postpartum anal sphincter lacerations in a population with minimal exposure to episiotomy and operative vaginal delivery.

This case-control study was designed to identify risk factors for anal sphincter lacerations (ASL) in a multicultural population where episiotomies and operative vaginal deliveries are rarely performed. Cases were subjects with ASL delivered between July 1997 and June 2003. Two controls were selected for each case matched for gestational age. Independent variables collected included age, race/ethnicity, parity, tobacco use, medical conditions, episiotomy, operative vaginal delivery, epidural use, and infant weight. One thousand and sixty-six subjects met the inclusion criteria. The risk of ASL increased with increasing maternal age (Odds ratio [OR] 1.09 per year, 95% confidence interval [CI] 1.06, 1.12) and increasing infant weight (OR 1.09 per 100 g, 95% CI 1.06, 1.13). Multiparity was protective (P1 vs P2 OR 0.19, 95% CI 0.13, 0.28, and > or =P3 vs P1 OR 0.04, 95% CI 0.02, 0.11). Hispanic and Native American women were at increased risk for ASL (OR 2.08, 95% CI 1.41, 3.09 and OR 1.92, 95% CI 1.07, 3.45, respectively).