The incidence of obstetric anal sphincter rupture in primiparous women: a comparison between two European delivery settings.

Background: During the last years, the incidence of obstetric anal sphincter rupture (OASR) has increased markedly in Sweden, and significantly less frequently in Italy. Our objective was to explore if different delivery management may explain the variation in OASR incidences.
Methods: In a retrospective study, data from 2,000 primiparous women in a Swedish and an Italian delivery unit were compared with respect to OASR, maternal age, gestational length, birth weight, labour induction, use of epidural analgesia (EDA) and oxytocin, vacuum extraction, episiotomy, and duration of the second stage of labour.
Results: Incidences of OASR were 9.2 and 0.4% in the Swedish and Italian centres, respectively. Other significant differences were noticed in maternal age, birth weight, gestational length, use of EDA, oxytocin, vacuum extraction, episiotomy, and frequency of induction. Further analysis of the Swedish population revealed a significant association between OASR and birth weight as well as vacuum extraction. The association with gestational age and duration of the second stage of labour approached significance level. However, no association could be found between OASR and maternal age, EDA, episiotomy or induction of labour.
Conclusion: Women delivering in the Swedish setting had a 23 times higher risk of OASR. An association between OASR and birth weight, gestational age, instrumental vaginal deliveries and duration of second stage was found. These factors varied between the settings and could possibly explain the differences in OASR incidence. The importance of alternative management, such as constant midwife support and perineal protection during delivery, may be a subject for further studies.