Increased risk of obstetric anal sphincter injury in women undergoing vaginal delivery after caesarean section: A systematic review and meta-analysis

Background: There is increased focus on obstetric anal sphincter injury (OASI) and there are several well-established risk factors such as birthweight, instrumental delivery and median episiotomy. Some studies have found increased risk of OASI in women delivering vaginally after a previous caesarean section (VBAC). Objective: To evaluate whether there is increased prevalence of OASI in VBAC compared with primiparous women. Search strategy: Literature search using PubMed, Embase and Cochrane databases. Selection criteria: All studies with data on both primiparous women and women undergoing VBAC were included. All included studies were evaluated using the "SIGN - methodology checklist" to verify if the quality was acceptable. Data collection and analysis: This systematic review included 23 articles conducted in 11 countries over 19 years. Included studies were analysed using RevMan version 5.4. Main results: We found increased prevalence of OASI in the VBAC group; 8.18% (95% confidence interval [CI] 8.07-8.29) compared with 6.59% (95% CI 6.56-6.62) in primiparous women. Correspondingly, the meta-analysis revealed increased prevalence for OASI in the VBAC group (odds ratio 1.27, 95% CI 1.10-1.47). We found a high level of heterogeneity (I-2 = 98%). Conclusion: Women undergoing VBAC had a higher prevalence of OASI compared with primiparous women.