Changing incidence of obstetric anal sphincter injuries-A result of formal prevention programs?

Obstetric anal sphincter injuries (OASIS) are serious complications to vaginal delivery causing anal incontinence in 50% of the women in the long term. In Norway, the incidence of OASIS has been significantly reduced from 4%-5% to 1%-2% after implementation of prevention programs focusing on perineal protection. The aim of our study was to evaluate whether implementation of formal prevention programs was associated with a reduced incidence of OASIS over time.

We performed a historical cohort study, evaluating incidence, change of incidence and risk factors of OASIS during the years 2011-2015 at the four delivery departments in the Capital Region of Denmark. Two of the four departments implemented formal prevention programs in 2012-2013. We performed trend tests and uni- and multivariable analyses, adjusting for important risk factors and calculating interactions between risk factors.

There were 75 173 vaginal deliveries during the study period; of those, 2670 (3.6%) were complicated by OASIS. The incidence of OASIS decreased during the study period from 4.3% (n = 636) in 2011 to 2.6% (n = 399) in 2015. There was a significant decrease in the incidence of OASIS at both the departments with formal prevention programs and those without. After adjustment for other important risk factors of OASIS, we found no significant difference in the risk reduction between departments with and without formal prevention programs.

We found that the general focus on prevention of OASIS in Denmark was associated with a significant decrease in the incidence of OASIS, but implementation of formal prevention programs did not lead to a further reduction. It is possible that more rigorous interventions at the hospitals with formal prevention programs could have resulted in a significant difference in incidence of OASIS.