Obstetric perineal injury: risk factors and strategies for prevention.

Fecal incontinence due to anal sphincter injury is the most important consequence of perineal trauma at vaginal delivery and may be of muscular or neurological origin. The risk of sphincter injury is increased at first delivery and in association with instrumental assistance, prolonged second stage, occipito-posterior position, and midline episiotomy, but is not predictable in individual cases. Injury can be prevented or minimized by enhancing uterine contractility during first labors, optimizing perineal repair technique, and by appropriate postnatal assessment of symptomatic women.