Cesarean Delivery and Anal Sphincter Injury MICHELLE FYNES, MD, VALERIE S. DONNELLY, MD, P. RONAN O’CONNELL, MD, AND COLM O’HERLIHY, MD Objective: Cesarean delivery has been thought to prevent all obstetric anal sphincter damage. The objective of this study was to determine the relationship between the timing of cesarean during primiparous delivery and injury to the anal sphincter mechanism. Methods: A prospective observational study was con- ducted, using a continence questionnaire and anorectal physiology assessment before and six weeks after primipa- rous delivery. A cohort of 234 women were recruited from the antenatal clinics at the National Maternity Hospital, Dublin. Thirty-four women delivered subsequently by ce- sarean, and 200 women by spontaneous vaginal delivery. Results: Thirty-four women underwent cesarean delivery without attempted vaginal delivery: eight prior to labor and 26 during labor, 17 in early labor (cervical dilatation less than 8 cm) and 9 in late labor (dilatation greater than 8 cm). No woman delivered by cesarean had altered fecal conti- nence postpartum. Anorectal physiology was unaltered in women delivered by elective cesarean or cesarean in early labor. Pudendal nerve terminal motor latency was pro- longed, anal squeeze pressure increment reduced, but vector symmetry index was unchanged in women delivered by cesarean delivery late in labor, indicating neurologic injury to the anal sphincter mechanism. Conclusion: Cesarean delivery performed in late labor, even in the absence of attempted vaginal delivery, does not protect the anal sphincter mechanism. (Obstet Gynecol 1998; 92:496 –500. © 1998 by The American College of Obstetri- cians and Gynecologists.) Obstetric injury is the most common factor that predis- poses to the development of fecal incontinence in wom- en. 1–7 Two mechanisms of injury are generally recog- nized: direct disruption of the anal sphincter muscles and traction neuropathy affecting the pudendal nerves. 1–6 The risk of sphincter disruption appears to be greatest during first vaginal delivery, whereas puden- dal neuropathy may be cumulative with successive deliveries. 8 Cesarean delivery has been thought to pro- tect against injury to the pelvic floor during parturition, but cesarean delivery late in labor does not avoid traction on the pudendal nerves 2,9,10 and may contrib- ute to a cumulative neuropathy. This is of particular importance in the obstetric management of women who have previously sustained pelvic floor injury or experi- enced altered continence after vaginal delivery. Previ- ous studies have not resolved the issue because of small numbers and inclusion of women of mixed parity and cases in which instrumental vaginal delivery had been attempted before cesarean delivery. The aim of this study was to determine the effects of cesarean delivery and, in particular, the timing of the cesarean during labor, on postpartum anal sphincter integrity and function in a large cohort of primiparous women in whom there had been no attempt at assisted or instrumental vaginal delivery, and to compare these effects with those of spontaneous unassisted vaginal delivery. Materials and Methods Between June 1993 and December 1994, a representative cohort of 350 nulliparous women were interviewed during the third trimester of pregnancy at the antenatal clinics of the National Maternity Hospital. Women with a past history of diabetes mellitus, anorectal disease, previous anorectal surgery, or preexisting irritable bowel syndrome were excluded. A total of 278 women agreed to participate and to return for postnatal assessment; subsequently, 200 women underwent spontaneous vaginal delivery and 15 women, cesarean delivery. Sixty-three women who had instrumental vaginal delivery were excluded be- cause of the recognized effects of instrumental delivery on anal sphincter integrity and fecal continence. 2,11,12 Based on a 90% power calculation designed to detect an actual difference of 25% with 90% confidence and a ratio of five controls per case, an additional 19 primiparous From the Department of Obstetrics and Gynaecology, University College Dublin, National Maternity Hospital, Dublin, and the Depart- ment of Surgery, Mater Misericordiae Hospital, Dublin, Ireland. This work was supported by the Irish Health Research Board and the Research Colleges of the National Maternity and Mater Misericordiae Hospitals. 496 0029-7844/98/$19.00 Obstetrics & Gynecology PII S0029-7844(98)00256-7