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 du ring vaginal delivery and to investigate the relation between different typ es 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 a nd Semmelweis Frauenklinic Wien between February and July 1999. The study w as restricted to a sample that included all women with uncomplicated pregna ncy as well as uncomplicated first and second stages of labor, gestational age > 37 weeks and a pregnancy with cephalic presentation. Women with multi ple gestations, noncephalic presentation, cesarean deliveries, shoulder dys tocia and gestational age less than or equal to 37 weeks were excluded from the study. RESULTS: Among the 1,118 births, 37 women (3.3%) experienced third-degree p erineal tears. The use of episiotomy per se and the type of episiotomy (mid line) as well as forceps delivery, primiparity, large infant head diameter, prolonged second stage of labor and use of oxytocin were identified as ris k factors for third-degree perineal tears during vaginal delivery. When ana lyzing different types of episiotomy, there was approximately a sixfold-hig her risk of third-degree perineal tears in women undergoing midline episiot omy as compared to mediolateral episiotomy. A stepwise logistic regression analysis revealed that episiotomy, prolonged second stage of labor and larg e infant head diameter remained independent risk factors for third-degree p erineal tears. CONCLUSION: We found several risk factors for third-degree perineal tears. The use of midline episiotomy was associated especially with an increased r isk of severe anal sphincter tears. To prevent women from long-term sequela e due to third-degree perineal tears, avoidable risk factors should be mini mized whenever possible.