Outcomes Following Obstetric Anal Sphincter Injury: Is There a Difference Between Subtypes in the Short Term?

Obstetric anal sphincter injuries (OASI) affect 2.9% of vaginal births and are associated with significant morbidity (Dudding et al. Ann Surg 247(2):224-237). Our objective was to evaluate if women sustaining minor OASI (3a) experience less pelvic floor dysfunction compared to major OASI (3b, 3c and 4).

In a tertiary Urogynaecology centre, patients were followed-up in a perineal clinic, with data regarding clinical outcomes recorded prospectively between 2011 and 2023. Patients graded bowel and urinary symptoms on a scale of 0-4. Pelvic floor muscle (PFM) strength, squeeze on per rectal (PR) examination and a Pescatori score were assigned by clinicians. Scores were retrospectively compared between minor and major tear groups. Statistical analysis was conducted using the chi-squared test for symptom scores and Mann-Whitney U test for PFM strength, Pescatori score and PR squeeze.

Data were complete for 1327 of 1455 women: 639 minor and 688 major tears. The majority of patients were asymptomatic or minimally symptomatic, 3 months postpartum, in respect to faecal passive incontinence, flatal incontinence and urinary symptoms with no difference between groups. There was no significant difference in Pescatori score, PFM strength or PR squeeze. There was a statistically significant difference between groups for faecal urgency (2.8% vs 5.1%, p = 0.0045) and faecal urgency incontinence (0.2% vs 1.2% p = 0.003).

Women sustaining minor OASI are less likely to experience faecal urgency and urgency incontinence than following major OASI. There was no significant difference for all other outcomes. Prospective studies using validated questionnaires with long-term follow-up are required to confirm our findings.