Risk factors for obstetric anal sphincter injuries and postpartum anal and urinary incontinence: a case-control trial

Obstetric anal sphincter injuries (OASIS) cause serious maternal morbidity for mothers. A clearer understanding of aetiological factors is needed. We aimed to determine the risk factors for OASIS . Birth details of 222 primiparous women sustaining OASIS were compared with 174 women who did not sustain OASIS (controls) to determine the relevant risk factors. The data underwent univariate analysis and logistic regression analysis. Asian or Indian ethnicity, operative vaginal birth (p = 0.00), persistent occipito-posterior position (p = 0.038) and rapid uncontrolled delivery of the head were identified as risk factors for OASIS. Pushing time, use of epidural, episiotomy and head circumference were not predictors of OASIS. Women with Asian or Indian ethnicity, operative vaginal birth, persistent occipito-posterior position and rapid uncontrolled delivery of the fetal head were likely to sustain OASIS. Awareness of these factors may help to minimise the incidence of OASIS.