The effect of childbirth on urinary incontinence: a matched cohort study in women aged 40-64 years

BACKGROUND: The relative impact of age, pregnancy and vaginal delivery on urinary incontinence is still an unresolved issue that involves the controversial question about the protective effect of cesarean delivery. OBJECTIVE: The purpose of this study was to estimate and compare the effect size of 1 pregnancy, 1 vaginal delivery, and the derived protective effect of cesarean delivery for different aspects of urinary incontinence in women 40-64 years old, all 20 years after birth. STUDY DESIGN: This Swedish nationwide matched cohort study involved 14,335 women. Data from 3 restricted, randomly selected, source cohorts of (1) nulliparous women who were unexposed to childbirth (n = 9136), (2) primiparous women who had experienced cesarean delivery and who had been exposed to 1 pregnancy (n = 1412), and (3) primiparous women who had been exposed to 1 pregnancy followed by vaginal delivery (n = 3787) were retrieved from The Swedish Medical Birth Register and Statistics Sweden and surveyed in 2008 and 2014, respectively. Parous women were all assessed 20 years postnatally. One-to-one matching with an interval for pairing of 3 years and 3 body mass index units was used in women 40-64 years old with information about body mass index (kilograms/square meters) and urinary incontinence. The procedure succeeded in 2630 of 2635 women (99.8%) and resulted in an adequate distribution of age and body mass index between groups. The surveys used a postal- and an internet-based questionnaire with validated questions for various aspects of urinary incontinence. Fisher's exact test and the Mann-Whitney U test were used for comparisons between matched groups; trend was analyzed with Mantel-Haenszel statistics. Predicted, age-related values of different aspects of urinary incontinence were obtained by logistic regression analysis. RESULTS: Pregnancy increased the prevalence of urinary incontinence from 20.1-30.1% (odds ratio, 1.71; 95% confidence interval, 1.43-2.05; P<.0001]. Urinary incontinence increased further after vaginal delivery to 43.0% (odds ratio, 1.75; 95% confidence interval, 1.49-2.05; P<.0001); "moderate" and "severe" urinary incontinence increased from 12.7-19.5% (odds ratio, 1.67; 95% confidence interval, 1.35-2.07; P<.0001). There was a parallel increase in urinary incontinence from 40-65 years of age in nulliparous and vaginally and cesarean delivered women. Cesarean delivery, compared with vaginal delivery, was associated with a 30.0% reduction of urinary incontinence (P<.0001) and a 35-52% reduction of more severe grades of urinary incontinence (P<.0001) and was unaffected by age. CONCLUSION: Both pregnancy and vaginal delivery incurred an increased risk of urinary incontinence in the long term. The age-related gap for urinary incontinence between nulliparous and primiparous women who were delivered by vaginal delivery or cesarean delivery was constant between parallel trajectories that spanned ages from 40-64 years. The calculated protective effect of cesarean delivery was unaltered and significant during the same age interval.