Most of the data about risk factors for urinary incontinence come from clinical trials or cross-sectional studies using survey design. Some risk factors were more rigorously studied than others. Thus, the information available is limited in its general applicability and one cannot infer causality from it. Despite these limitations, there is some evidence that age, pregnancy, childbirth, obesity, functional impairment, and cognitive impairment are associated with increased rates of incontinence or incontinence severity (16). Some factors pertain more to certain age groups than others. For example, in studies of older women, childbirth no longer increases the risk of incontinence, possibly because of the presence of comorbidities and other factors that promote incontinence. Medical diagnoses that were associated with urinary incontinence include diabetes, strokes, and spinal cord injuries. Other factors about which less is known or findings are contradictory include hysterectomy, constipation, occupational stressors, smoking, and genetics.
Pregnancy and delivery predispose women to stress urinary incontinence, at least during their younger years. Of women who have not borne children, those who are pregnant leak more often than their nonpregnant counterparts; about half of women report symptoms of stress urinary incontinence during pregnancy, but in most, the symptom resolves after delivery. In a prospective study, 32% of 305 primiparas developed stress urinary incontinence during pregnancy and 7% after delivery. By 1 year, only 3% reported stress urinary incontinence (24). However, 5 years later, 19% of women with no symptoms after the first delivery had stress urinary incontinence. Of women reporting stress urinary incontinence 3 months postpartum (in most of whom it had resolved by 1 year), 92% had such leakage 5 years later. Transient postpartum leakage may be a marker for future incontinence.
Various changes happen after delivery that may predispose women to stress urinary incontinence. Levator ani muscle strength decreases (25). About 20% of women develop a visible defect in the levator ani muscles after vaginal delivery (26). The bladder neck descends, and the pelvic muscles undergo partial denervation with pudendal neuropathy (27). In most studies, parity is strongly associated with urinary incontinence in younger women (28). In studies of women 60 years and older, parity is no longer an independent risk factor for incontinence (29). The reason for this is not well elucidated, but it may be because the changes in muscle, nerve, connective tissue, and hormonal function that occur with aging make other women “catch up” to those who developed incontinence at a younger age because of delivery trauma. Alternately, it may be that medical problems more common in older women account for a larger proportion of incontinence risk as women age.