Effect of dyssynergic defecation during pregnancy on third- and fourth-degree tear during a first vaginal delivery: a case-control study.

Objective: Determine whether dyssynergic defecation is a risk factor for third- or fourth-degree tear during a first vaginal delivery.

Study Design: A retrospective case-control study was conducted on 549 primiparous women. The case group (n = 140) sustained an anal sphincter tear and the control group (n = 409) had a perineal laceration lower or equal to a second-degree tear.