One-fourth of women on systemic estrogen reported vaginal bleeding and one-fifth reported breast tenderness during the trials.

The women in the largest study "were reportedly healthy, post-menopausal women and, on average, their incontinence got worse if they were allocated CEE. This is what the data show from a randomized trial ??” the best level of evidence for comparing different interventions," said Cody, who is also a member of the Academic Urology Unit at the University of Aberdeen.

Charla Blacker, M.D., of the Henry Ford Health System in Detroit, who did not take part in the review, said that doctors should take note that the way estrogen therapy is administered ??” by local estrogen therapy or systemic hormone treatments ??” could make a difference in whether incontinence improves or gets worse.

"These findings should be discussed with women who are contemplating using estrogen or hormonal therapy for relief of menopausal symptoms, particularly those who already have incontinence symptoms," Blacker said.

The Cochrane Library (thecochranelibrary) contains high quality health care information, including Systematic Reviews from The Cochrane Collaboration. These reviews bring together research on the effects of health care and are considered the gold standard for determining the relative effectiveness of different interventions. The Cochrane Collaboration (cochrane) is an international nonprofit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions.

Cody JD, et al. Oestrogen therapy for urinary incontinence in post-menopausal women. The Cochrane Database of Systematic Reviews 2009, Issue 4.