Venous Thrombosis and Conjugated Equine Estrogen in Women Without a Uterus | Venous Thromboembolism | JAMA Internal Medicine | JAMA Network
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Original Investigation
April 10, 2006

Venous Thrombosis and Conjugated Equine Estrogen in Women Without a Uterus

Author Affiliations

Author Affiliations: University of Hawaii and Pacific Health Research Institute, Honolulu (Dr Curb); Fred Hutchinson Cancer Research Center (Dr Prentice and Ms Rodabough) and University of Washington (Dr Prentice), Seattle, Wash; Baylor College of Medicine, Houston, Tex (Dr Bray); University of California at San Diego, La Jolla/Chula Vista (Dr Langer); Northwestern University, Evanston, Ill (Dr Van Horn); Medical College of Wisconsin, Milwaukee (Dr Barnabei); University of Nevada School of Medicine, Reno (Dr Bloch); Brown Medical School, Providence, RI (Dr Cyr); University of Cincinnati, Cincinnati, Ohio (Dr Gass); Boulder Women's Care, Boulder, Colo (Dr Lepine); Kaiser Permanente Division of Research, Oakland, Calif (Dr Sidney); MedStar Research Institute, Hyattsville, Md (Dr Uwaifo); and Leiden University Medical Center, Leiden, the Netherlands (Dr Rosendaal).

Arch Intern Med. 2006;166(7):772-780. doi:10.1001/archinte.166.7.772

Background  Postmenopausal hormone therapy has been associated with a 2- to 3-fold increased risk of venous thromboembolism (VT) (including deep vein thrombosis and pulmonary embolism) in observational studies and secondary prevention clinical trials. Clinical trial data on the effects of estrogen alone on VT are limited.

Methods  The Women's Health Initiative estrogen trial enrolled 10 739 women aged 50 to 79 years without a uterus. Participants were randomly assigned to receive conjugated equine estrogen (0.625 mg/d) or placebo.

Results  During a mean of 7.1 years, VT occurred in 111 women randomly assigned to receive estrogen (3.0 per 1000 person-years) and 86 randomly assigned to receive placebo (2.2 per 1000 person-years; hazard ratio, 1.32; 95% confidence interval, 0.99-1.75). Deep venous thrombosis was reported in 85 women randomly assigned to receive estrogen (2.3 per 1000 person-years) and 59 randomly assigned to receive placebo (1.5 per 1000 person-years; hazard ratio, 1.47; 95% confidence interval, 1.06-2.06). The VT risk was highest in the first 2 years. There were no significant interactions between estrogen use and age, body mass index, or most other VT risk factors. Comparison of Women's Health Initiative VT findings for estrogen and previous Women's Health Initiative findings for estrogen plus progestin showed that the hazard ratios for estrogen plus progestin were significantly higher than those for estrogen alone (P = .03), even after adjusting for VT risk factors.

Conclusion  An early increased VT risk is associated with use of estrogen, especially within the first 2 years, but this risk increase is less than that for estrogen plus progestin.