Pelvic floor disorders (PFDs) encompass a variety of symptoms and anatomical changes related to the genitourinary tract. Pelvic organ prolapse (POP), urinary incontinence (UI), and anal incontinence (AI) are the most common PFDs encountered in women. These disorders have a tremendous impact on a woman’s quality of life and function, and are associated with considerable healthcare costs. In this chapter, the epidemiology of PFDs will be discussed, focusing on three main topics: (1) prevalence and incidence; (2) nonmodifiable demographic risk factors, including age and race; and (3) economic impact.

Prevalence is defined as the total number of cases in a given population at a specific time divided by the number of individuals at risk for disease in the same population. Incidence, or incidence proportion, is defined as the number of new cases of disease that develop in a given population over a period of time divided by the total number of individuals followed for that same time period. The key distinction between these two epidemiologic concepts is that prevalence refers to all cases of disease while incidence refers to new cases of disease.

Defining Pelvic Floor Disorders

Although the concepts of prevalence and incidence may seem straightforward, rates vary widely based on the disease definition and study population. A major issue with determining the prevalence and incidence of PFDs is that each of these conditions is defined in a variety of ways—for example, POP can be diagnosed based on a physical examination or based on a questionnaire that addresses bothersome symptoms. Similarly, the prevalence of UI may be quite different when it is defined as the occurrence of involuntary leakage of urine in the last year versus the last month. The specific population studied can also impact prevalence and incidence. For example, the prevalence of AI will be different in a study of all adult community-dwelling women versus nursing home residents. In order to make meaningful determinations of prevalence and incidence, it is imperative to understand the disease definition and the population studied. This chapter will exclusively discuss the rates of PFDs in women in the United States.

Methods for measuring UI and overactive bladder (OAB) include the frequency of voids, frequency of incontinence episodes, volume of leakage, degree of bother, pad weight, urodynamic findings, clinically demonstrated leakage, or impact on quality of life. Similarly, for AI, the frequency of incontinence, type of stool and/or flatus lost, degree of bother, and impact on quality of life can also be used. Defining POP is equally varied, as it can be measured by symptoms, including frequency, duration, severity or degree of bother, as well as physical examination. Currently, the majority of research studies on POP rely on the pelvic organ prolapse quantification system (POP-Q);¹ however, the Baden Walker system is another method of prolapse assessment.² The use of validated questionnaires to assess symptoms, severity, degree of bother, and impact on quality of life has become a mainstay in urogynecologic studies.

Urinary Incontinence

Types of Urinary Incontinence

The type of UI impacts prevalence and incidence. UI, in general, is the symptom of involuntary urine loss.³ This symptom can be further characterized by the setting or activity during which urine loss occurs, such as with stress or urgency. Stress urinary incontinence (SUI) is the involuntary loss of urine with effort, physical exertion, sneezing, or coughing.³ Urgency urinary incontinence (UUI) is the involuntary loss of urine with urgency, and mixed urinary incontinence (MUI) is the loss of urine with urgency and effort, physical exertion, sneezing, or coughing.³ OAB syndrome is defined as urinary urgency, usually accompanied by frequency and nocturia, with or without UUI.³ Thus, OAB is more inclusive and includes UUI. Although there are other forms of UI, we will focus on SUI, UUI, and MUI, as these are the most common forms of incontinence. In the following sections, the prevalence and incidence of any type of UI will be discussed followed by a review for each type of UI.

Prevalence of Urinary Incontinence

Data from large epidemiologic studies, including the Women’s Health Initiative (WHI), National Health and Nutrition Examination Survey (NHANES), Group Health Cooperative (GHC), and Nurses’ Health Study (NHS), have reported prevalence rates of 5% to 64% for UI within the adult female population, using different definitions of disease based upon frequency of leakage (Table 1-1).^4-9 The broad range of reported prevalence is likely related to the definition of UI used in each study, as well as the age of the population studied. In the WHI, the prevalence of UI was 64%, as UI was defined as having ever leaked even a small amount of urine for this cohort of postmenopausal women.⁴ Comparatively, using data from NHANES that represents a similar age group, the prevalence of UI was 38% when UI was defined as difficulty controlling your bladder in the last 12 months.⁵ In this same population, when UI is stratified as every day, a few times a week, a few times a month, or a few times a year, the prevalence rates changed to 14%, 10%, 9%, and 5%, respectively.⁵ Similar variability in both definition and prevalence is demonstrated for UI in the GHC⁷ and NHS^8,9 as well (Table 1-1). When comparing the prevalence of UI in community-dwelling women to those living in long-term care facilities, UI is present in approximately 60% to 78% of nursing home residents.¹⁰

Incidence of Urinary Incontinence

In a systematic review performed by the Agency for Healthcare Research and Quality (AHRQ), the pooled annual incidence of UI was 6.25%, and there was a trend of increasing incidence rates associated with older age.¹⁰ The NHS demonstrated an increase in incidence with age as well only through age 50, with a subsequent slight decline in older women.¹¹ The two-year incidence of UI in women age 54 to 79 years in this study was 9.2%,⁸ whereas the two-year incidence in women age 36 to 55 years was 13.7%.¹¹

Prevalence of Stress and Mixed Urinary Incontinence

The prevalence of UI varies by type of UI. Overall, the prevalence of SUI across several large studies ranges from 5% to 51%, with considerable differences in the definition of disease (Table 1-2).^12-16 SUI is the most prevalent type of UI and occurs in 12.8% of women between 19 and 44 years and 21.5% in women between 45 and 64 years, whereas MUI is the most prevalent type in women over 65 years and occurs in 16.8% of women.¹⁰ Prevalence rates of 2% to 21% have been reported for MUI across all ages, again with notable differences in the definition of disease (Table 1-3).^7,13,14,16

Prevalence and Incidence of Overactive Bladder Syndrome and Urgency Urinary Incontinence

For OAB, the prevalence has been reported to range from 8% to 29%, depending upon the age and definition used (Table 1-4).^12,15,17 The reported range of prevalence is similarly broad for UUI from 2% to 49% and depends upon the definition of UUI (Table 1-4).^7,13-16 The incidence of UUI has been found to range from 0.3% to 0.7% per year.¹⁸

Remission of Urinary Incontinence

Reported remission for any UI is variable, and data on the regression of specific UI types are sparse. Assessment of remission rates is also further limited by the lack of data regarding the institution of therapy in studies evaluating remission or regression. Reported remission and improvement rates range from 2.0% for complete remission in the 54- to 79-year-old women to as high as 11.9% in 46- to 55-year-olds and 17.1% in 36- to 45-year-old women.^8,11

Surgery for Urinary Incontinence

Surgery for urinary incontinence is an important treatment option. The lifetime risk of surgery for UI or POP in women, given the average life expectancy of 79 years, is 11.1%.¹⁹ In a study of a large healthcare maintenance organization, the annual incidence of UI procedures increases with age from 0.4 per 10,000 women in those age 20 to 29 years to 31.9 per 10,000 women in those age 70 to 79 years.¹⁹ National data showed that approximately 130,000 women (rate 12 per 10,000) underwent inpatient SUI surgery in 2003.²⁰ Given the adoption of minimally invasive slings, outpatient SUI surgery has become more common, and in 2006, 105,656 women underwent outpatient UI surgery, an age-adjusted rate of 9.6 per 10,000 women.²¹

Pelvic Organ Prolapse

POP is the descent of one or more of the anterior or posterior vaginal walls, uterus, cervix, or apex of the vagina, associated with relevant symptoms.³ These symptoms include vaginal bulging; pelvic pressure; splinting or digitation; low backache; and bleeding, discharge, or infection related to dependent ulceration of the prolapse. POP can be further defined by the specific prolapsed compartment. Anterior vaginal wall prolapse is typically caused by prolapse of the bladder, whereas posterior vaginal wall prolapse is typically caused by rectal protrusion into the vagina.³ Vaginal vault prolapse is the descent of the vaginal cuff scar, versus the descent of the uterus or cervix.

Prevalence of Prolapse

The prevalence of symptomatic POP has been reported as low as 2.9% in a nationally representative survey of US women over the age of 20 years when the diagnosis was based entirely on the reported symptom of bulging or something visibly or palpably falling out (Table 1-5).⁶ In contrast, when prolapse was defined as any prolapse noted on examination, the prevalence was 41.2% in subjects with a uterus and 38% in subjects who had had a hysterectomy in postmenopausal women in WHI.²² The prevalence rates of prolapse vary considerably based on how prolapse is defined (Table 1-5).^{6,12,15,16,22,23} One particular challenge in defining prolapse is establishing the difference between “disease” and “normal,” as there may be some degree of prolapse that could be considered normal changes on examination, especially as a woman ages. Thus, it is important to assess symptoms and degree of bother when evaluating prolapse. A general principle is that women tend to report more bothersome symptoms as the vaginal wall approaches the hymen.²³