Fecal incontinence in nonpregnant nulliparous women aged 25 to 64 years-a randomly selected national cohort prevalence study.

Background: The extent to which fecal incontinence is associated with obstetrical history or pelvic floor injuries is still a controversial and unresolved issue. One crucial first step toward answering this question is the need to study fecal incontinence in nonpregnant, nulliparous women.

Objective: The aim of this study was to present detailed, descriptive measures of the accidental leakage of liquid or solid stool and gas in a randomly selected, large national cohort of nonpregnant, nulliparous women aged 25 to 64 years.

Study Design: The Swedish Total Population Register identified the source population. Four independent, age-stratified, simple random samples in a total of 20,000 nulliparous women aged 25 to 64 years were drawn from 625,810 eligible women. Information was collected in 2014 using postal and web-based questionnaires. The 40-item questionnaire included questions about the presence and frequency of the leakage of solid and liquid stool and gas, which provided the basis for the generic terms fecal and anal incontinence. Statistical analyses of the differences between the groups were performed using the Fisher's exact test for dichotomous variables and the Mann-Whitney U-test for continuous variables. The trend between >2 ordered categories of dichotomous variables was analyzed with Mantel-Haenszel statistics. When analyzing the trend between multiple ordered vs nonordered categorical variables, the Kruskal-Wallis test was used. The age-related probability and risk increase per 10 years for incontinence parameters was calculated from logistic regression models adjusted for body mass index.

Results: The study population was 9197 women, and the response rate was 52.2%, ranging from 44.7% in women aged 25 to 34 years to 62.4% among those from 55 to 64 years. All the types of incontinence, except severe isolated gas incontinence, increased with age up to 64 years. The estimated probability of fecal incontinence was 8.8% at age 25 years and 17.6% at age 64. The leakage of liquid stool was dominant, occurring in 93.1% (95% confidence interval, 91.4-94.5) of the women with fecal incontinence, whereas leakage of solid stool occurred in 33.9% (95% confidence interval, 31.1-36.7), of which approximately 80% also had concomitant leakage of liquid stool. The leakage of liquid stool increased markedly up to age 65, whereas the increase in the isolated leakage of solid stool was negligible across all ages (overall <0.4%). Liquid and solid stool, separate or in combination, co-occurred with gas in approximately 80%. The distribution pattern of the different types of leakage, single or combined, was similar in all the age groups. Both age and body mass index (kg/m) were risk factors for fecal incontinence (P<.0001), with an interaction effect of P=.16.

Conclusion: Abnormal stool consistency has been identified as the strongest risk factor for accidental bowel leakage. The same pattern characterized by a dominance of liquid stool and gas leakage, prevalent concomitant leakage of solid and liquid stool, and a negligible rate of isolated leakage of solid feces was observed across all ages. The low rates of isolated leakage of solid stool support the impression that dysfunction of the continence mechanism of the pelvic floor had a negligible role for bowel incontinence, which is essential information for comparison with women with birth-related injuries.