The consequences of undiagnosed obstetric anal sphincter injuries (OASIS) following vaginal delivery

Introduction and hypothesis We aimed to compare anal and urinary incontinence symptoms and anal manometry between women with undiagnosed obstetric anal sphincter injuries (OASIS) and women who had OASIS diagnosed and repaired. Methods This was a matched retrospective cohort study. Each missed OASI was matched with a diagnosed OASI for severity [minor (3a/b) or major (3c)], parity and length of follow-up. Women completed the modified St Mark's Incontinence Score and International Consultation on Incontinence Questionnaire. Women with OASIS or those without OASIS but with anal incontinence symptoms were seen in perineal clinic for perineal examinations, anorectal manometry and three-dimensional endoanal ultrasound 8-12 weeks postnatally or in a subsequent pregnancy. Results Forty missed OASIS were matched with 40 recognised OASIS (16 3a/b; 24 3c). The median modified St Mark's scores were higher for missed tears [11 (4, 15) vs. 1 (0, 4), p < 0.001] as well as the urinary incontinence scores [4 (0, 6) vs. 0 (0, 2), p = 0.01] than for the control group. Missed OASIS patients had a shorter perineal body [1.6 +/- 1.3 vs. 2.4 +/- 0.8, p = 0.009]. All missed OASIS had larger defects on endoanal ultrasound. One in four missed OASIS required further surgery [aOR 4.1 (95% CI 1.0-16.3), p = 0.04] and almost all needed colorectal input [aOR 24.1 (95% CI 7.3-80.0), p < 0.0001]. There were no differences in anal manometry. Conclusions Women with symptomatic missed OASIS are compromised in terms of anal and urinary incontinence symptoms, sphincter defect size and perineal body size requiring additional colorectal input. This highlights the importance of preventing OASIS and perseverance with training to diagnose OASIS.