Subsequent Pregnancy Outcomes After Obstetric Anal Sphincter Injuries (OASIS)

The rate of obstetric anal sphincter injuries (OASISs) at the time of vaginal delivery ranges from 0.0% to 23.9%. There is increasing evidence that OASIS can be prevented during birth by decreased use of 2 established risk factors for OASIS, use of episiotomies, and the use of forceps during operative vaginal deliveries. Few studies have investigated risk factors for recurrence of OASIS in a subsequent pregnancy. The aim of this retrospective study was to determine the rate of recurrent OASIS in women with a prior OASIS and to identify risk factors for recurrence. Participants were women who sustained an OASIS between November 2005 and March 2010 at a tertiary care hospital; data were obtained by review of their charts. A total of 1629 women had an OASIS, and 758 (46%) went on to have a subsequent pregnancy during the study period; 685 (90%) were delivered vaginally. Twenty-three (3.2%) of these women sustained a recurrent sphincter injury. Risk factors for recurrence included 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). Neither a history of a fourth-degree laceration, prior wound complications, or episiotomy at a subsequent delivery increased the risk of recurrence. These data show that the observed rate of recurrent OASIS was only 3.2% among women who subsequently delivered vaginally. Significant risk factors for recurrence were operative vaginal delivery and birth weight 4000 g or greater. Neither episiotomy at first delivery or at subsequent delivery increased recurrence risk.