Hormone replacement therapy (HRT), often prescribed to women during menopause, has been shown to increase the risk for venous thromboembolism (VTE). However, the effects of different types of HRT preparations on the risk of VTE have not been thoroughly investigated. This case-control study enrolled women between the ages of 40 and 79 years living in the United Kingdom who had a diagnosis of VTE (n=80,396), as well as controls who had no such diagnosis (n=391,494) to assess the association between risk of VTE and the use of different types of HRT. Researchers found that 7.2% of patients with a VTE had been exposed to HRT, as compared to 5.5% of controls. Oral HRT was associated with a significant increase in risk for VTE (OR 1.58, 95% CI 1.52 to 1.64) compared to individuals with no exposure, with results remaining significant upon stratifying patients that received estrogen-only preparations (OR 1.40, 95% CI 1.32 to 1.48) and combined preparations (OR 1.73, 95% CI 1.65 to 1.81). Of note, estradiol had a significantly lower risk than both equine estrogen (OR 0.85, 95% CI 0.76 to 0.95) and combined preparations (OR 0.83, 95% CI 0.76 to 0.91). The lowest risk for VTE of any of the oral preparations, when compared with no HRT, was found with the use of estradiol with dydrogesterone (OR 1.18, 95% CI 0.98 to 1.42). The highest risk was associated with medroxyprogesterone acetate (OR 2.10, 95% CI 1.92 to 2.31). Transdermal therapy did not increase the risk for VTE, as compared to no HRT (OR 0.93, 95% CI 0.87 to 1.01). Investigators therefore concluded that there were differences among HRT preparations in terms of VTE risk. Transdermal preparations were associated with no increased risk of this phenomenon.
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