Postmenopausal Estrogen Replacement Therapy and the Risk for Blood Clots: A Review from the U.S. Preventive Services Task Force

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The summary below is from the full report titled "Postmenopausal Estrogen Replacement and Risk for Venous Thromboembolism: A Systematic Review and Meta-Analysis for the U.S. Preventive Services Task Force." It is in the 7 May 2002 issue of Annals of Internal Medicine (volume 136, pages 680-690). The authors are J Miller, BKS Chan, and HD Nelson.

What is the problem and what is known about it so far?

After a woman stops menstruating (menopause), her body produces much less of the hormone estrogen. Lower estrogen levels can cause uncomfortable symptoms, such as hot flashes, and put women at risk for thinning of the bones (osteoporosis) and possibly some other medical conditions. Use of the hormone estrogen after menopause (postmenopausal estrogen replacement therapy) can decrease the uncomfortable symptoms of menopause and prevent osteoporosis. Hormone replacement therapy may also decrease the risk for some other conditions, such as heart disease and Alzheimer disease, but these effects are not yet proven. Postmenopausal estrogen replacement therapy has serious but infrequent side effects. Information about these side effects is important to consider in deciding whether hormone replacement is right for a particular woman. Blood clots (also known as thromboembolic disease) are potential side effects of estrogen therapy. Blood clots usually form in the deep veins of the leg, where they can cause pain and swelling. Pieces of blood clots in the leg can break off and travel to the lung, a condition called pulmonary embolism. A person who has pulmonary embolism can become very ill or even die.

Why did the authors do this review?

To better define the risk for thromboembolic disease in women taking postmenopausal estrogen replacement. The authors did this review for the U.S. Preventive Services Task Force. The Task Force is a group of health experts that reviews published research and makes recommendations about preventive health care.

How did the authors do this review?

Using MEDLINE, HealthSTAR, and the Cochrane Library databases (three large collections of medical articles that can be searched by computer), the authors identified articles about studies that reported thromboembolism as a side effect of estrogen replacement. The authors then combined the results of these studies to calculate the risk for developing thromboembolism.

What did the authors find?

After reviewing 12 studies, the authors estimated that for every 10,000 women who take estrogen replacement, about one and a half more women will develop a blood clot over the course of 1 year than among a similar group of women not taking estrogen. The risk for blood clots was highest in the first year of estrogen use. Risk for blood clots was also higher in women who had heart disease than in women who did not.

What are the implications of the review?

Women thinking about taking postmenopausal estrogen replacement should consider the risk for thromboembolism when weighing the pros and cons of this treatment.