Counseling women with obstetric anal sphincter injury - Risk of recurrence and the influence of mode of second delivery on subsequent anal incontinence - A systematic review and meta-analysis

Obstetric anal sphincter injury (OASI) is a severe complication of vaginal delivery. Up to 50% of women with OASI will experience anal incontinence at long-term. However, it is uncertain whether an elective cesarean section (CS) in a subsequent pregnancy following OASI decreases the risk of anal incontinence. The aim of this study was to assess the risk of recurrent OASI in a subsequent pregnancy after a first delivery with OASI. Additionally, we wanted to evaluate the impact of recurrent OASI on the risk of anal incontinence, and to determine whether the CS was protective against anal incontinence in women with a first delivery with OASI. Literature searches were made in PubMed, Cochrane, and Embase, the last search was made in May 2024. Studies were screened and study quality was assessed using "SIGN - Methodology Checklist". Thirteen studies (including 3 020 897 women) were included in the meta-analysis on risk of recurrent OASI. OASI in the first delivery increased the risk of recurrent OASI in the second delivery fivefold compared to women without previous OASI OR 4.9 (95%CI 4.0-5.9). The overall risk of acquiring a recurrent OASI was 6.1% (95%CI 5.9%-6.2%). Five studies (including 2 330 women) were included in the meta-analysis assessing the effect of mode of subsequent delivery on anal incontinence. The risk of anal incontinence was non-significantly increased in women with a second vaginal delivery OR 1.1 (95%CI 0.9-1.4). Four studies (including 2 300 women) were included in the meta-analysis on the risk of developing anal incontinence after recurrent OASI. The risk of anal incontinence was increased in women with recurrent OASI compared to women with OASI in the first delivery and a subsequent delivery without OASI OR 1.6 (95%CI 1.3-2.0). In conclusion, we found an increased risk of recurrent OASI in the second delivery for women with a previous OASI, compared to women without previous OASI. The risk of anal incontinence was increased in women with recurrent OASI. The risk of new onset or worsening of anal incontinence was not associated with mode of the second delivery. Women with previous OASI should be informed about the increased risk of recurrence and that elective CS is not necessarily protective against anal incontinence.