Effect of delivery on anal sphincter morphology and function

Anal sphincter injury is a serious complication of childbirth, which may result in persistent anal incontinence. Occult injuries, visualized with endoanal ultrasonography, have previously been reported in up to 35 percent of females in a British study. The aim of the present study was to study anal sphincter morphology and function before and after delivery in primiparous females in the United States.

Thirty-eight primiparous patients (mean age, 31 years) were evaluated with endoanal ultrasonography, anal manometry, and pudendal nerve terminal motor latency during pregnancy and after delivery. Bowel function before and after delivery was recorded according to set questionnaires. Cesarean section was performed in three patients.

Clinical sphincter tears, requiring primary repair, occurred in 15 percent of the patients. After delivery endoanal ultrasonography revealed disruptions in the external anal sphincter in six patients, but no patient had disruption in the internal anal sphincter. One patient had slight scarring in the external sphincter. Of the seven patients with pathologic findings at endoanal ultrasonography, the left pudendal latency increased after delivery (P < 0.05), and manometric results were reduced. Three of these seven patients had a third-degree or fourth-degree tear during delivery. All investigations were normal in the three patients who underwent cesarean section.

The present study demonstrates a significant frequency of sphincter injuries (20 percent) after vaginal delivery. Obstetricians should be aware of this risk and explicitly inquire about incontinence symptoms at follow-up after delivery.