High episiotomy rate protects from obstetric anal sphincter ruptures: a birth register-study on delivery intervention policies in Finland

To assess the impact of hospital episiotomy policy on obstetric and anal sphincter rupture (OASR, n = 2448) rates and risks among singleton vaginal deliveries in Finland between 1997 and 2007.

An observational, retrospective, population-based register study. All 424,297 women in hospitals with more than 1000 deliveries annually, were divided into three groups based on the episiotomy rate quartiles for 11 years and separated on the basis of whether the women were primiparous or multiparous. The lowest and the highest quartiles were compared against the hospitals with intermediate episiotomy rates, comprising the two quartiles around the median. Stepwise logistic regression analysis was used to adjust significant risk factors.

The annual range of episiotomy varied from 11 to 94% in primiparous women, and from 1 to 46% in multiparous women. After adjustment the risk of OASR appears to be 39% lower (OR 0.61, 95% CI 0.52-0.90) in primiparous and 45% lower (OR 0.55, 95% CI 0.42-0.72) in multiparous women delivered in the highest quartile hospitals. At an individual level, episiotomy was a protective factor (OR 0.82, 95% CI 0.75-0.91) in primiparous women, but increased the risk by 2.36-fold in multiparous women (OR 2.36, 95% CI 1.86-2.84).

The results suggest that high episiotomy rate provided protection from OASR among both groups of women. Among the multiparous women, the 2.4-fold risk of OASR related to episiotomy at an individual level might be explained by confounding by indication, since episiotomy was performed more often to women at a high risk of OASR.