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

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 section.

The purpose was to estimate and compare the effect size of one pregnancy, one vaginal delivery, and the derived protective effect of cesarean section for different aspects of urinary incontinence in women aged between 40 to 65 years, all 20 years after birth.

This Swedish, nationwide matched cohort study involved 14,335 women. Three restricted, randomly selected, source cohorts of nulliparous women, unexposed to childbirth (n=9,136), one-para cesarean delivered women, exposed to one pregnancy (n=1,412), and one-para exposed to one pregnancy followed by vaginal delivery (n=3,787) 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 three years and three BMI units was used in women aged 40 to 64 years with information about BMI (kg/m2) and urinary incontinence. The procedure succeeded in 2,630 out of 2,635 women (99.8%), resulting in an adequate distribution of age and BMI 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 was used for comparisons between matched groups and trend was analysed with Mantel-Haenszel statistics. Predicted, age-related values of different aspects of urinary incontinence were obtained by logistic regression analysis.

Pregnancy increased the prevalence of urinary incontinence from 20.1% to 30.1% (odds ratio [OR], 1.71; 95% confidence interval [CI], 1.43-2.05, P< .0001]. Urinary incontinence increased further after vaginal delivery to 43.0% (OR, 1.75; 95% CI, 1.49-2.05; P< .0001) and 'Moderate and Severe' urinary incontinence from 12.7% to 19.5% (OR, 1.67; 95% CI, 1.35-2.07; P < .0001). There was a parallel increase in urinary incontinence from 40 to 65 years in nulliparous, vaginally and cesarean delivered women. Cesarean section compared to vaginal delivery was associated with a 30.0% reduction of urinary incontinence (P< .0001) and 35% to 52% reduction of more severe grades of urinary incontinence (P< .0001) and was unaffected by age.

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 one-para women delivered by vaginal delivery or cesarean section was constant between parallel trajectories that spanned ages between 40 and 65 years. The calculated protective effect of cesarean section was unaltered and significant during the same age interval.

American journal of obstetrics and gynecology. 2019 May 20 [Epub ahead of print]

Maria Gyhagen, Sigvard Åkervall, Mattias Molin, Ian Milsom

Gothenburg Continence Research Centre, Institute of Clinical Sciences, Sahlgrenska Academy at Gothenburg University, Gothenburg; Department of Obstetrics and Gynecology, Södra Älvsborgs Hospital, Borås. Electronic address: ., Gothenburg Continence Research Centre, Institute of Clinical Sciences, Sahlgrenska Academy at Gothenburg University, Gothenburg., Statistical Consultancy Group, Gothenburg., Department of Obstetrics and Gynecology, Sahlgrenska University Hospital, Gothenburg, Sweden.