Recurrence of obstetric third-degree and fourth-degree anal sphincter injuries

To examine outcomes after primary obstetric anal sphincter injuries in a subsequent pregnancy.

This was a retrospective analysis of prospectively collated data from a large perinatal database between 2006 and 2010. Primiparous vaginal deliveries with an obstetric anal sphincter injury were identified and tracked to identify their subsequent delivery characteristics and perineal outcomes.

A primary obstetric anal sphincter injury occurred in 5.3% of primiparous vaginal deliveries (9,857/186,239); of those patients, 2,093 had a subsequent delivery, and 91.9% delivered vaginally (1,923/2,093). The recurrent obstetric anal sphincter injury rate was also found to be 5.3% (102/1,923). The adjusted odds ratios (ORs) for primary obstetric anal sphincter injuries were significantly increased in large-for-gestational-age neonates for both third-degree laceration (adjusted OR 2.1, 95% confidence interval [CI] 1.9-2.2) and fourth-degree laceration (adjusted OR 2.7, 95% CI 2.3-3.1) and almost all obstetric interventions studied. The adjusted ORs for recurrent obstetric anal sphincter injuries were significant for large-for-gestational-age (25/102, adjusted OR 2.2, 95% CI 1.3-3.6) and instrumental deliveries (15/102, adjusted OR 2.4, 95% CI 1.2-4.6).

In this study population, the incidence of recurrent obstetric anal sphincter injuries was similar to that of primary obstetric anal sphincter injuries, and most patients went on to deliver vaginally for subsequent deliveries. The risk of recurrent obstetric anal sphincter injuries was doubled in those who delivered a large-for-gestational-age neonate and in those who had an instrumental delivery.