Risk factors for rupture of the anal sphincter

To evaluate risk factors for rupture of the anal sphincter during vaginal delivery.

All 292 parturients with rupture of the anal sphincter in four neighbouring central hospitals in southern Sweden between 1988 and 1990 were identified retrospectively. For each case a control was selected, the sole matching criterion being that the control woman was the next to give birth vaginally in the same unit as the case. Only singleton deliveries were included. For comparison of risk factors among cases and controls, McNemar's test was used for bivariate testing; multiple regression analysis was restricted to those variables found to be significant in the bivariate analysis. Odds ratios (OR) were calculated with 95% confidence limits (CL).

In all, 292 of 22,653 deliveries (1.3%) had a rupture of the anal sphincter. Of a total of 14 independent variables explored, 8 were found to be significantly associated with rupture of the anal sphincter in the bivariate testing. In the following multivariate analysis, three variables remained significantly associated with rupture of the anal sphincter: birthweight > or = 4000 g (OR 2.6; CL 1.7, 3.9), primiparity (OR 2.2; CL 1.5, 3.3) and episiotomy (OR 1.7; CL 1.1, 2.6).

Episiotomy appears to be significantly associated with rupture of the anal sphincter. In contrast to primiparity and birthweight, the incidence of episiotomy during vaginal delivery may easily be reduced. However, only a prospective, controlled study will disclose the true negative or positive effects of episiotomy.