Hormone therapy and risk of venous thromboembolism among postmenopausal women.

Venous thromboembolism, either deep vein thrombosis or pulmonary embolism, is a serious side-effect of postmenopausal hormone therapy. Current use of oral estrogens increases the risk of venous thromboembolism, especially during the first year of treatment, but past users of hormone therapy have a similar risk as never-users. Among women at high risk for venous thromboembolism (for example, thrombogenic mutations, obesity), oral estrogens use further enhances the thrombotic risk. Recent studies have shown that transdermal estrogens might be safe with respect to thrombotic risk. The difference in thrombotic risk between oral and transdermal estrogens may be partially explained by changes in hemostasis. Few data are currently available regarding the impact of progestogens on venous thromboembolism risk, but norpregnane derivatives might be thrombogenic. Individual assessment of the benefit-risk ratio is needed before initiating treatment and oral estrogens should be avoided among women at high risk for venous thromboembolism.