OBSTETRIC EVENTS LEADING TO ANAL-SPHINCTER DAMAGE

Objective: To identify the obstetric factors relating to anal sphincte r injury at first vaginal delivery by prospective cohort study of prim iparous women. Methods: We compared the results of a bowel function qu estionnaire and anal vector manometry before and 6 weeks after deliver y in 184 primiparous women. Postpartum, pudendal nerve conduction late ncy was measured in all women, and anal endosonography was performed i n 81 with altered fecal continence or abnormal physiology. Results: Si xteen (9%) women, none of whom had altered fecal continence, were deli vered by cesarean. After vaginal delivery, 42 of 168 (25%) women had i mpairment of fecal continence and 76 of 168 (45%) women had abnormal a nal physiology. Instrumental vaginal delivery was associated with an 8 .1-fold (95% confidence interval [CI] 2.7, 24.0; P < .001) risk of ana l sphincter injury and a 7.2-fold (95% CI 2.8, 18.6; P < .001) risk of symptoms. Duration of the second stage of labor beyond 60 minutes led to a 1.7-fold (95% CI 1.14, 2.48; P < .01) risk of anal sphincter inj ury and a 1.6-fold (95% CI 1.03, 2.6, P = .01) risk of symptoms. Epidu ral analgesia, used in 58% of vaginal deliveries, prolonged the second stage of labor (P = .004; odds ratio [OR] 7.7; 95% CI 4.0, 14.7) and was associated with increased risk of sphincter injury (P = .02; OR 2. 1; 95% CI 1.1, 4.0) and of symptoms (P = .02; OR 2.0; 95% CI 1.1, 3.7) . Conclusion: Instrumental delivery and a second stage of labor prolon ged by epidural analgesia are the obstetric factors that pose the grea test risk of injury to the anal sphincter mechanism in primiparous vag inal delivery. (Obstet Gynecol 1998;92:955-61. (C) 1998 by The America n College of Obstetricians and Gynecologists.).