Which factors are associated with anal incontinence after obstetric anal sphincter injury?

Obstetric anal sphincter injury (OASI) is an important factor in the etiology of anal incontinence. This study aimed to evaluate whether anal sphincter defects, levator avulsion or levator ballooning after OASI are associated with severity of anal incontinence. Furthermore, we evaluated whether factors such as constipation and altered stool consistency are associated with symptoms of incontinence after OASI.

In this multicenter prospective observational cohort study, women with OASI were invited to participate at least 3 months after primary repair. All women completed validated questionnaires, including St Mark's incontinence score, Bristol stool scale (BSS) and Cleveland clinic constipation score (CCCS), and underwent four-dimensional (4D) transperineal ultrasound for assessment of the levator ani muscle and anal sphincter.

In total, 220 women were included. Median follow-up was 4 months (range, 3-98 months). Univariate linear regression analysis showed an association of St Mark's incontinence score with a residual defect of the external anal sphincter (EAS) (β, 1.55 (95% CI, 0.04-3.07); P = 0.045), higher parity (β, 0.85 (95% CI, 0.02-1.67); P = 0.046), BSS (β, 1.28 (95% CI, 0.67-1.89); P < 0.001) and CCCS (β, 0.36 (95% CI, 0.18-0.54); P < 0.001). However, multivariate linear regression found an association of St Mark's incontinence score only with BSS (β, 1.50 (95% CI, 0.90-2.11); P < 0.001) and CCCS (β, 0.46 (95% CI, 0.29-0.63); P < 0.001).

Residual defects of the EAS, detected on 4D transperineal ultrasound, are associated with severity of anal incontinence symptoms measured using St Mark's incontinence score 4 months after OASI repair. Furthermore, clinical factors such as constipation and altered stool consistency appear to influence this association and may therefore play a more important role in clinical management. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.