Intervention during labor: risk factors associated with complete tear of the anal sphincter.

Among 41,200 consecutive deliveries there were 152 cases of complete tear of the anal sphincter (complete tear). In a case-control design, the association between interventions during labor (forceps, vacuum extraction, use of oxytocin and prostaglandins and mediolateral episiotomy) and complete tear, were evaluated by confounder control using multiple logistic regression analysis. Controls chosen were the patients delivering just before and after the index patient with complete tear. Use of Kielland forceps, mediolateral episiotomy, shoulder dystocia and nulliparity were significantly associated with complete tear. Maternal age, presentation in labor, duration of second stage of labor and the indication for instrumental deliveries and episiotomy had no significant association with complete tear.