Risk factors for obstetric anal sphincter injuries during vaginal delivery: can we reduce the burden?

Third- and fourth-degree perineal tears are associated with significant discomfort and impact on women's quality of life after labor. We reviewed the literature on risk factors for obstetric anal sphincter injuries (OASIS), focusing on modifiable risk factors for OASIS to help obstetricians prevent them. Methods: We searched MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, and Scopus using key search terms. We selected clinical studies, systematic reviews, and meta-analyses in English investigating antepartum and intrapartum factors associated with OASIS. Three researchers independently se- lected studies and documented outcomes. Results: We identified forty-two relevant articles for inclusion. Among antepartum fac- tors, primiparity, neonatal birth weight, and ethnicity were associ- ated with a higher risk of OASIS. Instrumental delivery, midline epi- siotomy, duration of the second stage of labor, persistent occiput posterior position, and labor augmentation were those intrapartum factors reported associated with OASIS. Conclusions: Multiple ante- and intrapartum factors are associated with a higher risk of OASIS. The actual modifiable factor is episiotomy during the second stage of labor. However, literature reporting episiotomy associated with a re- duction in OASIS prevalence during instrumental delivery is limited. These results may help obstetricians recognize women at higher risk of developing severe perineal tears and recommend further investi- gation on the role of episiotomy in an operative delivery.