OBJECTIVE: The purpose of this study was to better understand associations among age, race, obstetric history, and urinary incontinence in women.

STUDY DESIGN: Race and obstetric history were assessed through the use of biennial mailed questionnaires from 1976 to 1996 among participants of the Nurses' Health Study. In 1996, 83,168 women aged 50 to 75 years reported their frequency of leaking urine and quantity leaked. We used logistic regression to calculate multivariate-adjusted odds ratios and 95% CIs for the relation of risk factors to leaking urine.

RESULTS: Overall, 34.1% of the women reported leaking urine at least once per month during the previous 12 months; this prevalence was lowest in the black women (21.2%). After potential confounders were controlled, there were strong trends of increasing prevalence of occasional and frequent leaking with increasing age (P trend <.0001). There was also increasing prevalence of leaking urine with increasing parity; for example, compared with nulliparous women, the odds ratio for frequent leaking was 1.72 (95% CI, 1.55-1.90) among those with ≥5 births. Odds ratios that were associated with parity were higher in women aged <60 years than in women aged ≥60 years. Age at first birth of >35 years was associated with a slight elevation in frequent leaking compared with women with age at first birth from 21 to 25 years but was stronger for women with age at first birth of <21 years (OR, 1.27; 95% CI, 1.13-1.42).

CONCLUSION: In these women, leaking urine is common; this condition is most prevalent in white women, in older women, in parous women, and in women with a younger age at first birth.