Estrogen therapy may increase the risk of venous thrombosis, the formation of blood clots in the veins, among postmenopausal women who have had their uterus removed, according to a study in the April 10 issue of Archives of Internal Medicine.
Venous thromboembolism (VT), which includes the conditions deep vein thrombosis (a blood clot in a deep vein) and pulmonary embolism (a blood clot that travels to the lungs), affects about one adult per 1,000 years of life, according to background information in the article. Researchers suspect that hormone therapy may increase a woman's risk of developing VT. The largest study analyzing the relationship between hormone therapy and VT is the Women's Health Initiative (WHI), which included two large clinical trials. One WHI trial examined the effects of estrogen plus progestin and found that this combination of hormones appeared to increase the risk of VT.
J. David Curb, M.D., University of Hawaii and Pacific Health Research Institute, Honolulu, and colleagues analyzed data from the other WHI trial, in which the effect of estrogen alone was studied in 10,739 women aged 50 to 79 years. The participants were randomly assigned to take either combined equine estrogens (a mix of several estrogens) or placebo. They were followed for an average of 7.1 years, during which 197 women developed VT, including 144 with deep vein thrombosis, 91 with pulmonary embolism and 38 with both.