Risk factors for primary and subsequent anal sphincter lacerations: a comparison of cohorts by parity and prior mode of delivery

At this institution, women undergoing VBAC are at similarly high risk of anal sphincter laceration, compared with nulliparous women. Women with prior anal sphincter laceration are at 3 times increased risk for subsequent sphincter laceration, compared with women with prior vaginal delivery without sphincter laceration. Pregnancy by itself does not appear to be an important factor in decreasing the risk of anal sphincter laceration in subsequent deliveries.