Cesarean delivery and anal sphincter injury

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.

A prospective observational study was conducted, using a continence questionnaire and anorectal physiology assessment before and six weeks after primiparous delivery. A cohort of 234 women were recruited from the antenatal clinics at the National Maternity Hospital, Dublin. Thirty-four women delivered subsequently by cesarean, and 200 women by spontaneous vaginal delivery.

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 continence postpartum. Anorectal physiology was unaltered in women delivered by elective cesarean or cesarean in early labor. Pudendal nerve terminal motor latency was prolonged, 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.

Cesarean delivery performed in late labor, even in the absence of attempted vaginal delivery, does not protect the anal sphincter mechanism.