P209 - Understanding OASIS: Risk Factors, Ultrasound Detection, and Personalized Postpartum Counseling for Future Childbirth Decisions

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Purpose/Background: Obstetric anal sphincter injury (OASIS) are serious issues during vaginal births that can affect a woman's quality of life may limit future childbearing options. Early diagnosis of OASIS is crucial to prevent deterioration of sphincter damage, provide postpartum support, and ensure proper prenatal counseling for future pregnancies. The study aims to assess risk factors and the predictive value of endoanal ultrasound (EAUS) in detecting OASIS in women who had vaginal deliveries at a tertiary Pelvic Floor Disorders center.

Methods/Interventions: A retrospective study was conducted at Guy’s and St Thomas’ Hospital in London, UK. Data collected from 2008 to 2023. Variables included age, parity, history of episiotomy, extent of tear, birthweight, incontinence flatus, passive faecal, and urge faecal incontinence symptoms. In the first part of the study, we examined in a multivariate analysis the factors associated with the development of OASIS. Then we evaluated the ability to detect OASIS using EAUS and subsequently assessed where the different types of injuries tend to localize within the external and internal anal sphincter.

Results/Outcomes: The data included 1,506 women who underwent vaginal birth, with 78 missing ultrasound scores, leaving 1,428 for analysis. These women underwent EAUS and manometry exams at a median of 14.4 weeks post-delivery (IQR: 13.1 to 17.7 weeks). We examined the associations between patient factors and ultrasound-detected OASIS. Multivariable analysis found that assisted delivery (OR 2.95), flatus incontinence (OR 1.42), low resting pressure (OR 1), and low squeeze pressure (OR 1) were independently associated with OASIS. The tear severity was assessed clinically and by EAUS, and their agreement was analyzed. Clinically, 3% of women had no OASIS, compared to 27% by EAUS. Level 3a tears were identified in 8.9% clinically, but 18.5% via EAUS. The weighted kappa method indicated a kappa value of 0.20 (95% CI: 0.17 to 0.23), suggesting poor to fair agreement between the two methods. We also studied association between the type of defect detected by US and the longitudinally extension of involvement of anal sphincters. There was no association between lesion type (scarring or defects) and the extent of external anal sphincter involvement. However, scarring was more common in the lower section of the internal anal sphincter (50%) than defects (4%) (p=0.03).

Conclusion/Discussion: In conclusion, key risk factors for OASIS in women undergoing vaginal deliveries have been identified,helping to target those at risk for anal incontinence. Close monitoring with proctological exams and EAUS, which detects subtle injuries more effectively, allows for early intervention and personalized counseling, empowering informed decisions on future childbirth options.