IMR Press / CEOG / Volume 48 / Issue 6 / DOI: 10.31083/j.ceog4806201
Open Access Review
Risk factors for obstetric anal sphincter injuries during vaginal delivery: can we reduce the burden?
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1 Department of Obstetrics and Gynecology, University of Verona, 37126 Verona, Italy
2 Department of Surgery, University of Verona, 37126 Verona, Italy
*Correspondence: (Simone Garzon)
Clin. Exp. Obstet. Gynecol. 2021, 48(6), 1267–1272;
Submitted: 13 August 2021 | Revised: 7 September 2021 | Accepted: 21 October 2021 | Published: 15 December 2021
Copyright: © 2021 The Author(s). Published by IMR Press.
This is an open access article under the CC BY 4.0 license (

Background: 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 selected studies and documented outcomes. Results: We identified forty-two relevant articles for inclusion. Among antepartum factors, primiparity, neonatal birth weight, and ethnicity were associated with a higher risk of OASIS. Instrumental delivery, midline episiotomy, 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 reduction 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 investigation on the role of episiotomy in an operative delivery.

Obstetric anal sphincter injury
Perineal tears
Obstetric trauma
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