Third degree obstetric perineal tears: risk factors and the preventive role of mediolateral episiotomy.

Objective: To determine risk factors for third degree obstetric perineal tears and to give recommendations for prevention.

Design: Retrospective case control study.

Setting: A teaching hospital in The Netherlands.

Participants And Methods: One hundred and twenty cases of vaginal delivery complicated by third degree perineal tear and 702 uncomplicated vaginal deliveries were compared, with respect to possible risk factors.

Results: In a multivariate model high birthweight, forceps delivery, induced labour, epidural anaesthesia and parity were risk factors for anal sphincter tear. In addition, mediolateral episiotomy was associated with fewer sphincter injuries. Separate analysis of nulli- and multiparous women demonstrated that high birthweight and epidural anaesthesia (increased risk) and mediolateral episiotomy (decreased risk) were factors associated with anal sphincter tear only in nulliparous women.

Conclusions: We found several risk factors for anal sphincter tear. Nulliparous women are at higher risk than multiparous women. Mediolateral episiotomy may be sphincter-saving especially in nulliparous women and therefore prevent them from chronic faecal incontinence.