Mode of delivery and maternal outcome in subsequent delivery after an obstetric anal sphincter injury: a Finnish retrospective cohort study

Background Obstetric anal sphincter injury (OASI) is a severe complication of vaginal delivery. In previous studies, parturients with a preceding OASI are at increased risk of a recurrent OASI (rOASI) in subsequent vaginal deliveries. In Finland, the rate of OASI is low compared to other countries, at 1.4% of deliveries, and the incidence of rOASI is not well-known. This study examined recurrence and mode of delivery after an OASI. Methods This historical cohort study includes 278 women who have experienced an OASI and have delivered again in Tampere University Hospital. Deliveries complicated by an rOASI were compared to those without an rOASI, and women planning a cesarean delivery (CD) for their subsequent delivery were compared to women planning a vaginal delivery. Risk factors for OASI were explored by comparing deliveries complicated by an OASI to all deliveries. Results After an OASI, 78.1% of parturients planned a vaginal delivery and 21.9% a cesarean delivery (CD). Vaginal delivery was successful in 98.1% of cases and only 1.9% of parturients who underwent vaginal delivery experienced an rOASI. Due to the low incidence rate, no risk factors for rOASI could be identified. Parturients were most likely to have a CD in their subsequent delivery when the delivery complicated by an OASI was induced, the second stage was prolonged, episiotomy was performed, or the delivery had been assisted. The most common indication for CD was maternal request or fear of childbirth (85.9%). Assisted vaginal delivery, birthweight > 4,000 g, episiotomy, and postterm pregnancy were more common in deliveries complicated by OASI compared to all other vaginal deliveries in the study hospital during the same time period. Conclusions The recurrence rate of OASI was low and the vaginal uncomplicated delivery rate was high among women who chose it for their subsequent delivery after an OASI.