Progestogens and venous thromboembolism among postmenopausal women using hormone therapy.

Hormone therapy (HT) is the most effective treatment for correcting menopausal symptoms after menopause. HT initially consisted of estrogens alone and progestogens were secondly added to estrogens for preventing the risk of endometrial cancer associated to estrogens use. Venous thromboembolism (VTE), including deep vein thrombosis and pulmonary embolism, is a major harmful effect of HT. It is now well known that oral and transdermal estrogens are differentially associated with VTE risk but progestogens may be another important determinant of the thrombotic risk among HT users. Both randomized controlled trials and meta-analysis of observational studies suggested that the VTE risk was higher among users of estrogens plus progestogens than among users of estrogens alone. With respect to the different pharmacological classes of progestogens, there is evidence for a deleterious effect of medroxyprogesterone acetate on VTE risk. In addition, observational studies showed that norpregnane derivatives were significantly associated with an increased VTE risk whereas micronized progesterone could be safe with respect to thrombotic risk. The effect of tibolone on VTE risk remains uncertain. In conclusion, progestogens may have differential effects on VTE risk according to the molecules and therefore represent an important potential determinant of the thrombotic risk among postmenopausal women using estrogens.