A prospective study of anal sphincter injury due to childbirth

Background: Faecal incontinence commonly affects women, principally because of childbirth. Our aims were to determine the functional effect of childbirth on the pressures generated by the anal sphincter and to determine the patterns of injury to the sphincter. Methods: Anal manometry was performed in 53 primiparous women prenatally, in 50 women at a median of 5 weeks postnatally, and repeated in 26 women at a median of 6 months postnatally. In addition, anal ultrasound was performed postnatally. Pelvic floor symptoms were assessed. The mode of delivery was examined to determine what variables affected anal function. Results: Squeeze pressure was significantly reduced (P < 0.001) 6 weeks postnatally (mean, 170.4 cm H₂O; standard deviation (s), 56) compared with the prenatal value (mean, 225.6 cm H₂O; s, 58). This occurred in symptomatic and asymptomatic women and in women with a normal anal ultrasound. Resting pressure was significantly reduced at 6 weeks (P < 0.001; prenatal mean, 91.6 cm H₂O; s, 25; postnatal mean, 80.0 cm H₂O; s, 21). Delivery method (vaginal or caesarean) was the only factor significant for the reduced squeeze pressure (r= 53.377; standard error, 13.973; P < 0.001). Sphincter defects (41%) were common but did not influence anal sphincter function. Conclusion: Anal function was significantly affected by vaginal delivery with short-duration follow-up. This occurred with and without evidence of an anal sphincter injury. The importance of a sphincter injury is questioned.