Risk factors for third-degree perineal tears in vaginal delivery, with an analysis of episiotomy types

OBJECTIVE: To determine the risk factors for third-degree perineal tears during vaginal delivery and to investigate the relation between different types of episiotomy and the occurrence of such tears. STUDY DESIGN: This retrospective multicenter study consisted of an analysis of data from the delivery databases of the University Hospital of Vienna and Semmelweis Frauenklinic Wien between February and July 1999. The study was restricted to a sample that included all women with uncomplicated pregnancy as well as uncomplicated first and second stages of labor, gestational age > 37 weeks and a pregnancy with cephalic presentation. Women with multiple gestations, noncephalic presentation, cesarean deliveries, shoulder dystocia and gestational age < or = 37 weeks were excluded from the study. RESULTS: Among the 1,118 births, 37 women (3.3%) experienced third-degree perineal tears. The use of episiotomy per se and the type of episiotomy (midline) as well as forceps delivery, primiparity, large infant head diameter, prolonged second stage of labor and use of oxytocin were identified as risk factors for third-degree perineal tears during vaginal delivery. When analyzing different types of episiotomy, there was approximately a sixfold-higher risk of third-degree perineal tears in women undergoing midline episiotomy as compared to mediolateral episiotomy. A stepwise logistic regression analysis revealed that episiotomy, prolonged second stage of labor and large infant head diameter remained independent risk factors for third-degree perineal tears. CONCLUSION: We found several risk factors for third-degree perineal tears. The use of midline episiotomy was associated especially with an increased risk of severe anal sphincter tears. To prevent women from long-term sequelae due to third-degree perineal tears, avoidable risk factors should be minimized whenever possible.