Risk factors for obstetric anal sphincter injuries (OASI) at a tertiary centre in south India

Despite several studies that have reported risk factors for obstetric anal sphincter injuries (OASI), data from the Indian subcontinent are scarce. The purpose of this study was to identify risk factors for these sphincter injuries in an Indian population.

This was a case-control study within a retrospective cohort of vaginal deliveries at a tertiary care facility. All vaginal births beyond 24 completed weeks of gestation and birth weight ≥500 g from January 2008 to December 2012 were identified from the hospital electronic database. Cases were women with OASI sustained during vaginal delivery; the rest constituted controls. Potential risk factors for occurrence and severity of OASI were assessed initially using bivariate analysis and then a logistic regression model.

The incidence of sphincter injury was 2.1% of vaginal births and 1.1% of all deliveries, and major-degree (3c and 4th-degree) tears constituted 20.9% of tears. After adjusted analysis, significant predictors for injury included primiparity, delivery at or beyond 41 weeks of gestation, epidural analgesia, instrumental delivery, shoulder dystocia, birth weight ≥4000 g, and head circumference ≥35 cm. Episiotomy protected against sphincter injuries, particularly in forceps and ventouse deliveries. Shoulder dystocia was significantly associated with major-degree tears, while episiotomy appeared to be protective.

Risk factors are similar to those in other population groups; however, primiparity appears to be associated with lesser risk and forceps delivery with greater risk of sphincter trauma than previously reported.