Maternal Ethnicity and the Risk of Obstetrical Anal Sphincter Injury: A Retrospective Cohort Study

To explore the role of maternal ethnicity as a risk factor for obstetrical anal sphincter injury (OASI). A retrospective cohort study of all women with singleton gestations who had a vaginal delivery at term, between January 2014 and October 2017, at a single center. OASI was defined as a third-degree perineal tear (anal sphincter complex) or a fourth-degree perineal tear (anorectal mucosa). The characteristics of women with and without OASIs were compared. Multiple logistic regression was performed to account for potential confounders, including ethnicity. During the study period, 11 012 women were eligible for inclusion, of whom 336 (3.1%) had an OASI; 313 (93.1%) had a third-degree tear, and 23 (6.9%) had a fourth-degree tear. Women with OASIs were characterized by younger maternal age (