Body mass index, waist circumference, and urinary incontinence in midlife: A follow‐up of mothers in the Danish National Birth Cohort

Background Obesity is a modifiable risk factor for urinary incontinence, yet few studies have investigated how waist circumference as compared to body mass index (BMI) influences the risk of urinary incontinence. Objective To estimate how BMI and waist circumference associates with risk of urinary incontinence in midlife and determine which of the two is the strongest predictor of urinary incontinence. Methods Cohort study among mothers in the Danish National Birth Cohort. Weight and waist circumference were self‐reported 7 years after cohort entry. Symptoms of urinary incontinence in midlife were self‐reported using the International Consultation on Incontinence Questionnaire Female Lower Urinary Tract Symptoms (ICIQ‐FLUTS) and analyzed continuously and as presence or absence of any, stress (SUI), urgency (UUI), and mixed (MUI) urinary incontinence. Linear and log binomial regressions were used to calculate mean differences and risk ratios (RR) with 95% confidence intervals (CI). Restricted cubic splines were generated to explore nonlinear relationships. Results Among 27 254 women at a mean age of 44.2 years, any urinary incontinence was reported by 32.1%, SUI by 20.9%, UUI by 2.4%, and MUI by 8.6%. For all outcomes, increases in risk were similar with higher BMI and waist circumference. The estimates of association were strongest for MUI (RR 1.10, 95% CI 1.08;1.12 and RR 1.12, 95% CI 1.10;1.14 for half a standard deviation increase in BMI and waist circumference, respectively). While increases in risk of the other outcomes were seen across the entire range of BMI and waist circumference, the risk of SUI rose until BMI 28 kg/m2 (waist circumference 95 cm), and then fell slightly. Conclusions Symptoms of urinary incontinence and prevalence of any urinary incontinence, SUI, UUI, and MUI increased with higher BMI and waist circumference. Self‐reported BMI and waist circumference were equally predictive of urinary incontinence.