Background: Anal sphincter rupture is a serious complication of vaginal delivery and almost half the affected women have persistent defecatory symptoms despite adequate primary repair. During the past decade, the incidence of anal sphincter ruptures has been increasing in Sweden and is currently estimated to occur in 2.5% of vaginal deliveries. The aim of the study was to report the frequency of anal sphincter ruptures in two university hospitals in two Scandinavian countries, Malmö in Sweden and Turku in Finland, and analyze the potential determinants.
Methods: Retrospective analysis of a population of 30,933 deliveries (26,541 vaginal) during the years 1990 to 1994.
Results: The incidence of anal sphincter ruptures in Malmö, Sweden was 2.69%, and in Turku, Finland 0.36%. There were no significant population differences for the known risk factors (fetal weight, nulliparity or fetal head circumference). However, there is a difference in manual support given to the perineum and to the baby's head when crowning through the vaginal introitus between Malmö and Turku. The proportion of operative vaginal deliveries and abnormal presentations was significantly higher in Turku reflected in the lower Apgar score at 5 minutes and longer duration of second phase of labor. When high risk deliveries (operative vaginal delivery, abnormal presentation and newborns over 4,000 g) were excluded, the risk for anal sphincter ruptures was estimated to be 13 times higher in Malmö than in Turku.
Conclusions: The difference in the incidence of anal sphincter rupture between Malmö, Sweden and Turku, Finland may be due to the difference in manual control of the baby's head when crowning.