The increased incidence of obstetric anal sphincter rupture--an emerging trend in Finland

To describe recent trends in the prevalence and risk factors of obstetric anal sphincter ruptures during between 1997 and 2007 in Finland.

We analyzed a population-based register of 514,741 women with singleton vaginal deliveries recorded in the Finnish Medical Birth Register. Primiparous (n=2315) and multiparous women (n=534) with anal rupture compared in terms of possible risk factors to primiparous (n=215,463) and multiparous (n=296,429) women without anal rupture, respectively, using stepwise logistic regression analysis.

The occurrence of anal rupture increased from 0.5% in 1997-1999 to 1.8% in 2006-2007 among primiparous women, and from 0.1% in 1997-2001 to 0.3% in 2006-2007 among multiparous women. Over the study period, the likelihood of women having anal rupture in these groups increased by a factor of 3.28 (95% CI 2.86-3.76) and 2.83 (95% CI 2.19-3.67), respectively, after adjustments for strong associations with many known risks. Changes in population characteristics and in the use of interventions were small, and these did not cause the increased anal rupture rate. The only exception was vacuum-assisted deliveries, which explained about 9% of the rising anal rupture risk.

The current obstetric practice is not optimal for protecting the perineum and reflects the need to standardise obstetric care.