Lacerations of the anal sphincter or injury to sphincter innervation during childbirth are major causes of fecal incontinence, but the incidence and importance of occult sphincter damage during routine vaginal delivery are unknown. We sought to determine the incidence of damage to the anal sphincter and the relation of injury to symptoms, anorectal physiologic function, and the mode of delivery. We studied 202 consecutive women six weeks before delivery, 150 of them six weeks after delivery, and 32 with abnormal findings six months after delivery. Symptoms of anal incontinence and fecal urgency were assessed, and anal endosonography, manometry, perineometry, and measurement of the terminal motor latency of the pudendal nerves were performed. Ten of the 79 primiparous women (13 percent) and 11 of the 48 multiparous women (23 percent) who delivered vaginally had anal incontinence or fecal urgency when studied six weeks after delivery. Twenty-eight of the 79 primiparous women (35 percent) had a sphincter defect on endosonography at six weeks; the defect persisted in all 22 women studied at six months. Of the 48 multiparous women, 19 (40 percent) had a sphincter defect before delivery and 21 (44 percent) afterward. None of the 23 women who underwent cesarean section had a new sphincter defect after delivery. Eight of the 10 women who underwent forceps delivery had sphincter defects, but none of the 5 women who underwent vacuum extractions had such defects. Internal-sphincter defects were associated with a significantly lower mean (+/- SD) resting anal pressure (61 +/- 11 vs. 48 +/- 10 mm Hg, P < 0.001) six weeks post partum, and external-sphincter defects were associated with a significantly lower squeeze pressure (increase above resting pressure, 70 +/- 38 vs. 44 +/- 13 mm Hg; P < 0.001). There was a strong association (P < 0.001) between sphincter defects and the development of bowel symptoms. Occult sphincter defects are common after vaginal delivery, especially forceps delivery, and are often associated with disturbance of bowel function.
