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Urinary incontinence is a dynamic condition that can progress and regress, but few studies have examined risk factors for change in incontinence status.
Stratified random sampling was used to construct a racially/ethnically diverse, population-based cohort of 2109 women age 40 to 69 years old. Data were collected by questionnaires and review of medical records. A second survey, approximately 5 years later, was completed by 1413 (67%) of the original cohort. Frequency of urinary incontinence was categorized as ‘<weekly,’ ‘weekly’ and ‘daily.’ Change in incontinence status was defined as ‘new onset’ incontinence, ‘progression’ or ‘regression ‘of incontinence between frequency categories, and ‘resolution’ of incontinence. Predictor variables included demographics, body mass index (BMI) and other medical conditions. Logistic regression was used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (95% CIs).
Compared to white, non-Hispanic women, African-American women were less likely to have progression of incontinence (OR= 0.46, 95% CI=0.24–0.88). New onset of incontinence was more common in women with higher BMI at baseline (p=0.006), who experienced an increase in BMI (p=0.03) or a decline in general health (p=0.007) during the study. Participants with COPD at baseline were more likely to report progression of incontinence (OR=2.64, 95% CI=1.22–5.70). Type of baseline incontinence was not significantly associated with risk of change in continence status independent of frequency.
Identifying risk factors for change in incontinence status may be important in developing interventions to reduce the burden of incontinence in the general population.
Most epidemiologic studies of urinary incontinence are cross-sectional or retrospective, with relatively few prospective longitudinal studies of the incidence of urinary incontinence. Of the handful of population-based studies reporting incidence incontinence, most have been limited to European women or American women of European descent. In additional, the few longitudinal studies generally report on risk factors for new onset (incident) urinary incontinence, but not for progression or resolution of existing incontinence. This distinction is important as prognostic risk factors may differ from risk factors for incident disease. In addition, only a few studies have reported on change by incontinence type (stress, urgency and mixed). No study could be located which examined the association between type of incontinence at baseline and change in incontinence status in a multivariate model.
We sought to determine factors that predict incidence, progress, regression and resolution of urinary incontinence among the diverse women participants in a prospective cohort study, the Reproductive Risks for Incontinence Study at Kaiser (RRISK).
RRISK is a prospective cohort study of women who were at baseline members of Kaiser Permanente Medical Care Program of Northern California (KPNC), a pre-paid group practice with over 3 million members which provides comprehensive health care to about 25% of general geographic population in the area served. Previous studies have found members of KPNC to somewhat under represent the very poor and very wealthy and to be slightly more educated compared to the general population in the same geographic area, but to be very similar with respect to other demographic characteristics.1 The study was approved by the institutional review (human subjects) boards of both the University of California, San Francisco and Kaiser Foundation Research Institute. A random sample of 10,161 women between 40 and 69 years of age as of January 1, 1999 who had been members since age 18 was generated from membership files. Starting in September 1999, women were screened and recruited with the goal of obtaining weighted sample with equal numbers in each 5 year age strata and a distribution of 40% white, 20% Hispanic, 20% Asian and 20% African-American participants.2 Women were excluded if they did not speak English or Spanish, reported having had less than half of their births within KPNC, were no longer members of KPNC, had moved out of the area, or were demented or otherwise too impaired to participate. Among the 8835 women whose eligibility could be determined, 6018 (68%) were ineligible, primarily for having < 50% of their births within Kaiser (n=2451) or because we had already filled their age-race strata (n=2632), and 2817 (32%) were eligible. Assuming that 32% of women of unknown eligibility were also ineligible, the total number of eligible women would be 3240, of which we enrolled 2109 (65.1%). A second survey conducted approximately 5 years later, between June, 2003 to January 2008, was completed by 1413 (67%) of the original cohort. Of the 696 women not completing the second survey, 446 refused, 163 were ineligible due to poor health or having moved outside the area, and 87 could not be contacted.
During the first (baseline) survey, variables ascertained by pre-interview and in-person questionnaires included demographic characteristics, past history of incontinence, diabetes, chronic obstructive pulmonary disease (COPD) and hysterectomy, pregnancy and parturition history, menopausal status, smoking, and general health, and a detailed description of current incontinence symptoms. Weight and height were measured by the interviewer and used to calculated body mass index (BMI) in kg/m2. Ambulation speed was measured by recording the time needed to walk10 feet, turn around, and return. The second (follow-up) survey ascertained an interim medical, surgical, and pregnancy history, and repeated measures of menopausal status, smoking, general health, BMI, and ambulation speed.
For both surveys, current urinary incontinence was defined as at least monthly incontinence and was further characterized as ‘less then weekly,’ ‘weekly’ and ‘daily.’ Type of incontinence was defined for those women with at least weekly incontinence, according to their response to two questions, one asking if incontinence occurred “with an activity like coughing, lifting, sneezing or exercise” (stress incontinence) and the other asking if incontinence occurred “with a physical sense of urgency” (urgency incontinence). Women were classified as having stress incontinence if they reported the majority of episodes being stress incontinence, and as having urgency incontinence if they reported the majority of the episodes being urgency incontinence. Those reporting both stress and urgency incontinence with neither predominating were classified as mixed incontinence. Women with only other incontinence (n=34) were excluded from the analyses by incontinence type.
Change in incontinence status was defined as incident incontinence (change from continence to any degree of incontinence); progression of incontinence (change from ‘< weekly incontinence’ to ‘weekly or daily incontinence,’ or from ‘weekly incontinence’ to ‘daily incontinence’); regression of incontinence (change from ‘weekly incontinence’ to ‘< weekly incontinence’ or from ‘daily incontinence’ to ‘weekly or < weekly incontinence’); and resolution of incontinence (change from any degree of incontinence to continence). A logistic model was used to test the association between candidate risk variables and change in incontinence status. Variables were evaluated for inclusion in the multivariate model using backwards elimination, and were retained in the final model if p remained <0.2. Continuous variables were also examined as categorical variables to evaluate for non-linear associations with change in incontinence status. Parity was categorized as 0, 1 or 2+ as there was virtually no additional association between number of deliveries beyond the second and change in incontinence status. Each model included only women for whom the specific change in continence status was possible. For example, the model for progression of incontinence was limited to women with incontinence < daily incontinence at baseline and the dependent variable was therefore women who had progression of their incontinence vs. all other women in this group. Associations between independent variables and change in incontinence were expressed as odds ratio (OR), and 95% confidence intervals (95% CI). All p-values were two-sided. Model fit was assessed using the Hosmer-Lemeshow ‘goodness of fit’ test and the c statistic.3 All analyses were carried out in SAS Version 8.02 (SAS Institute, Cary, NC).
Table 1 shows characteristics of the 2109 women in the original cohort and the 1413 women who completed baseline and follow-up surveys. The only significant differences are that the longitudinal group had slightly fewer women who were current smokers (8% vs. 10%) and who had less than a high school education (17% vs. 20%). As shown in Table 2, nearly 73% of women reported at least 1 episode of leakage in the past 12 months at baseline. Change in continence status was reported by 536 women (38%) of women, with progression being the most common change, followed by resolution, regression, and new onset.
Figure 1 shows the transitions of incontinence status from baseline to 5-year follow-up. Among the 386 women who were continent at baseline, 31% reported new incontinence at follow-up, though this was mostly limited to mild incontinence (< weekly), with less than 4% reporting weekly or daily incontinence. Progression of incontinence was reported by 20% of the 862 women with weekly or < weekly incontinence at baseline; regression of incontinence was reported by 31% of the 390 women with weekly or daily incontinence at baseline. Of the 1027 women with some degree of incontinence at baseline 12% reported resolution of incontinence at 5-year follow-up. Resolution varied by baseline incontinence frequency ranging from 18% of women with incontinence < weekly, to less than 2% of women with weekly incontinence. Figure 2 shows change in type of incontinence for women with incontinence once a week or more often. Women with urgency incontinence were least likely to change type of incontinence or to report less than weekly incontinence at follow-up while women with mixed incontinence at baseline were most likely to change type or to report less than weekly incontinence. The incidence of new incontinence by age group varied by type of incontinence, as seen in Figure 3. While the incidence of both urgency and mixed incontinence increased across all 3 age groups, the incidence of stress incontinence was actually the lowest in the middle age group.
Variables associated with change in incontinence status in the unadjusted (bivariate) analysis at p<0.2 are presented in Table 3 and were retained in the multivariate models if they were associated with the dependent variable at p<.20. Table 4 shows the associations which were significant at p<0.05 in the multivariate models for change in incontinence. All models show acceptable fit based on their c statistic and Hosmer-Lemeshow p-value. African-American women incontinent at baseline were less likely than white, non-Hispanic women to report progression of incontinence. Women with higher income were significantly less likely to have new incontinence. Parous women were more likely to have regression of incontinence. Women with higher BMI at baseline were more likely to have new onset of incontinence during the next 5 years and women who experienced an increase in their BMI over the study period were significantly more likely to have new onset of incontinence and less likely to have regression of existing incontinence. Women reporting excellent general health at baseline were more likely to experience resolution of incontinence over the course of the study while women who had a decline in general health were more likely to have new onset incontinence.
We also compared progression, regression and resolution of incontinence by type of baseline incontinence. Women with stress incontinence at baseline were somewhat more likely to report progression (30.3%) compared to those with urgency (24.7%) or mixed incontinence (24.3%), and women with mixed incontinence were more likely to report regression (38.4%) compared to women with stress (29.0%) or urgency incontinence (30.2%). However these differences were not statistically significant either unadjusted or after adjustment for other risk factors.
This study is the first population-based study of incident urinary incontinence with substantial proportions of Hispanic, Asian, and African-American women, and one of the few studies examining risk factors for progression and regression of incontinence. Women in our cohort reported an incidence of new incontinence of 31% over approximately 5 years (about 6% per year). This is consistent with a recent review of 10 population-based studies that found the incidence of incontinence in middle-aged and older women to range from 4 to 11% with a median of about 7%.4
While incidence increased with age for urgency and mixed incontinence, the incidence of stress incontinence was lowest in the middle age group. This finding is consistent with previous studies that have found a reduction in the prevalence of stress incontinence with age in middle-aged and older women.5–8 and an inverse association of age with new stress incontinence.5 We also found an average rate of remission of about 2.4% per year, which is at the lower end of what has been previously reported.4,5,9,10
The findings from multivariate analysis of risk factors generally support and extent associations reported in previous studies. African-American women were significantly less likely to report progression of incontinence than white, non-Hispanic women. While previous studies have found an association between race and new onset of incontinence,7,9 no study could be located that reported on race and progression of incontinence.
A higher BMI at baseline was associated with a lower chance of resolution of incontinence, and women who experienced an increase in BMI were more likely to report new onset and less likely to report regression of incontinence. This is consistent with previous observational studies that have found an increase in BMI to be associated with increased risk of new onset incontinence,11, 12 and a randomized controlled trial that found that weight loss is associated with regression and resolution of incontinence.13 Better general health at baseline predicted resolution of incontinence while women continent at baseline but whose general health declined with were more likely to have new onset of incontinence. This is consistent with previous studies which found general health to be inversely associated with the risk of incontinence.12,15
We also found an adjusted association between change in continence status and COPD at baseline, but not with other co-morbidities. We could not find any studies reporting on COPD and change in incontinence status, though population-based studies have reported an association between COPD and prevalent incontinence.16,17 Diabetes at baseline was not associated with change in incontinence in the multivariate models. Other studies have also failed to find a significant association between diabetes and incident incontinence. 7,9,12,14,15 This lack of significant association may be due to a lack of power or because the association depends on diabetes severity, duration, or other characteristics that were not included in our data. Hysterectomy, heart disease, and urinary tract infections at baseline or in the past year were also not associated with change in incontinence status. This is consistent with previous reports finding no association between new incontinence and hysterectomy, 18,19 heart disease,5,15 or recent urinary tract infections.5
All types of incontinence were associated with risk of progression and resolution of incontinence, reflecting primarily an association with incontinence frequency (weekly or greater vs. less than weekly), with no significant association with UI type per se. However, our study was not powered to compare change in incontinence status by type of baseline incontinence, so these results should not be taken as evidence that there is in fact no association.
Several aspects of the study should be kept in mind when interpreting our findings. Data were ascertained for the most part by self-report. To the extent that self-report is not reliable, associations may be underestimated due to misclassification. However, self-report may best represent urinary incontinence from the patient’s perspective and conducting a similarly sized study with a detailed urogynecologic exam is not feasible. We examined associations for multiple risk factors, increasing the chance that some association would be found by chance. Finally, the study had limited precision for some comparisons due to the small number of women in some categories
Our study provides additional information on the dynamic change in urinary incontinence in a diverse, population-representative sample of women. We identified several independent factors that affect the development of incident incontinence and progression or remission of existing incontinence. Distinguishing factors for progression and regression from those for new onset may be useful in investigating the etiology of progression and regression of urinary incontinence. It is also important in designing interventions for preventing progression on incontinence in women who already have the condition.
The Reproductive Risk of Incontinence Study in Kaiser (RRISK)was funded by the National Institutes of Diabetes and Digestive and Kidney Diseases Grant # R01- DK53335 and the NIDDK/Office of Research on Women’s Health Specialized Center of Research Grant # P50-DK064538