Sex Difference in Risk of Second but Not of First Venous Thrombosis

The risk of recurrent venous thrombosis is 2-fold higher in men than in women. In contrast, no such sex difference in the risk of first venous thrombosis has been reported. We hypothesized that, for a first event, a risk difference between the sexes is masked by female exposure to reproductive factors (oral contraception, pregnancy/puerperium, and postmenopausal hormone therapy).From the Multiple Environmental and Genetic Assessment of Risk...