Risk factors for female anal incontinence: New insight through the Evanston-Northwestern Twin Sisters Study

OBJECTIVE: To evaluate risk factors for anal incontinence using an identical twin sisters study design to provide control over genetic variance. METHODS: A total of 271 identical twin sister pairs (mean age 47 years) completed the validated Colorectal Anal Distress Inventory questionnaire detailing the presence and severity of anal incontinence. Data were analyzed using a stepwise logistic regression with repeated binary measures to account for correlated data within twin pairs. Three different statistical models were used to analyze nonobstetric as well as obstetric risk factors separately. RESULTS: Significant risk factors for anal incontinence and higher Colorectal Anal Distress Inventory anal incontinence subscale scores included age 40 years or older (fecal: odds ratio [OR] 2.82, 95% confidence interval [CI] 1.21-6.0; flatal: OR 1.90, 95% CI 1.11-3.24), menopause (fecal: OR 2.10, 95% CI 1.15-3.8; flatal: OR 2.11, 95% CI 1.43-3.13), increasing parity (parity ≥ 2; fecal: OR 3.09, 95% CI 1.25-7.65; flatal: OR 2.72, 95% CI 1.65-4.51), and the presence of stress urinary incontinence (fecal: OR 2.11, 95% CI 1.12-3.98; flatal: OR 1.72, 95% CI 1.14-2.59). Obesity was associated with significantly higher Colorectal Anal Distress Inventory anal incontinence subscale scores (mean difference 5.18, P = .007). Cesarean delivery after initiation of labor was associated with a lower prevalence of anal incontinence than vaginal birth; however, this difference was not statistically significant (17% compared with 4%, P = .11). No anal incontinence was noted in women who had only elective cesarean deliveries. CONCLUSION: Age, menopause, obesity, parity, and stress urinary incontinence are the major risk factors for female anal incontinence.