Body mass index and complications after obstetric anal sphincter injury, 8 weeks postpartum

Introduction and hypothesis The impact of body mass index (BMI) on pelvic floor recovery after an obstetric anal sphincter injury (OASI) is unclear. The aim of this study was to evaluate the hypothesis that urinary incontinence (UI) and anal incontinence (AI) are more common in overweight and obese women than in normal-weight women 8 weeks postpartum in women with OASI. Methods A population-based cohort study including 6,595 primiparous women, with an OASI, delivered between 2014 and 2019. Exposure and questionnaire data were retrieved from the Swedish Perineal Laceration Registry. Uni- and multivariate analyses were used to compare normal-weight (BMI ≤24.9, reference), overweight (25.0–29.9), and obese (≥ 30) women with regard to UI and AI at 8 weeks post-partum. Results Multivariate analyses showed an increased risk for urinary incontinence (OR 1.54, 95% CI 1.27–1.87) among overweight women as well as among obese women (OR 1.72, 95% CI 1.32–2.24). In contrast to our hypothesis, both overweight women (OR 0.68, 95% CI 0.56–0.83) and obese women (OR 0.65, 95% CI 0.49–0.87) were at a decreased risk for any gas and/or faecal incontinence after adjustment to possible confounding factors. The absolute rate of AI was 40.1% among normal-weight women, 34.2% among overweight women, and 29.1% in the obese group. Conclusions Urinary incontinence is more common, whereas AI is less common among overweight and obese women than in primiparous women with a BMI <24.9, 8 weeks after an OASI. The new finding, that overweight women report less AI than normal-weight women, merits further study.