Subsequent Pregnancy Outcomes After Obstetric Anal Sphincter Injuries (OASIS)

Objectives: To describe obstetric outcomes in women with a prior obstetric anal sphincter injury (OASIS) and to identify risk factors for recurrence. Methods: A retrospective chart review of women who sustained an OASIS between November 2005 and March 2010 at a tertiary care hospital was performed to identify risk factors for recurrence. Results: One thousand six hundred twenty-nine patients had an OASIS. Of these, 758 patients (90%) subsequently delivered during the aforementioned timeframe; 685 patients had a subsequent vaginal delivery. Of the women, 3.2% had a recurrent OASIS. Recurrence was associated with larger birth weight (27% >= 4000 g vs 11.6% <4000 g; P = 0.04) and delivery mode (25.0%, 12.5%, and 2.7% for forceps-assisted, vacuum-assisted, and spontaneous deliveries, respectively (P = 0.0001)), whereas a history of fourth-degree laceration, prior wound complication, or episiotomy at subsequent delivery were not (P = 0.5, P = 0.5, and P = 0.4, respectively). Conclusions: Recurrent OASIS occurred in a small percentage of women (3.2%) who subsequently delivered vaginally. Recurrent OASIS was associated with operative vaginal delivery and birth weight 4000 g or greater. Neither episiotomy at first delivery nor at subsequent delivery conferred an increased recurrence risk.