Conduct of labor and rupture of the sphincter ani

To determine whether the conduct of the second stage of labor and delivery technique influences the incidence of rupture of the anal sphincter.

A total of 1072 primipara delivered vaginally at term at Rigshospitalet in 1998. A questionnaire on prenatal risk factors, conduct of the second stage of labor, and delivery technique was completed by the attending midwife immediately after delivery in 90 cases with rupture of the sphincter and in two subsequent controls (n = 164), matched by use of vacuum extractor and episiotomy.

Partial or total sphincter rupture was found in 8.4% of primipara who delivered vaginally, in 20.9% of those delivered by vacuum extraction, and in 6.4% of those with episiotomy only. The prenatal risk factors--maternal age, birth weight, shoulder dystocia, and edema of the perineum were found to have a statistically significant effect on the incidence of rupture of the sphincter ani. In non-instrumental vaginal deliveries easing of the perineum over the caput as it advanced helped prevent a rupture of the anal sphincter. Vacuum extraction performed with the woman in a semi-recumbant position was associated with an increased risk of rupture of the anal sphincter, whereas attention to the perineum during extraction decreased the risk.

The significant effect of prenatal risk factors did not explain a correlation between delivery technique and rupture of the sphincter ani. The present study indicates that a reduction in the incidence of sphincter rupture may be accomplished by improved obstetric care: fewer vacuum extractions and improved delivery technique.