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Objectives: To evaluate the prevalence of obstetrical anal sphincter injuries (OASIS), which include third and fourth degree perineal tears in primigravida in routine versus selective mediolateral episiotomy. Secondly, to determine the rate of episiotomy in local settings.

Methods: This randomized control trial was carried out in the labor ward of a tertiary hospital of the Universiti Kebangsaan Malaysia Medical Center, Kuala Lumpur, Malaysia between May and October 2009. The trial included 171 primigravida beyond 38 weeks gestation who achieved vaginal delivery, and randomly assigned to selective and routine episiotomy groups. The type of perineal injuries following childbirth among 171 women were evaluated.

Results: The overall episiotomy rate from both groups was 76.6%. The prevalence of third degree perineal tears was 3.7% in the routine compared with selective mediolateral episiotomy at 1.1%. There was no occurrence of fourth degree tears in both groups. However, selective mediolateral episiotomy was associated with an increased risk of periurethral and labial injury compared with the routine group (4.5% versus 0%).

Conclusion: Routine mediolateral episiotomy in primigravida is associated with a higher prevalence of obstetrical anal sphincter injuries. As anal sphincter injuries are known to have morbidities, selective mediolateral episiotomy in primigravida is therefore recommended in the implementation of new delivery practice, and in an attempt to reduce our high episiotomy rate.