A lower risk of recurrent venous thrombosis in women compared with men is explained by sex-specific risk factors at time of first venous thrombosis in thrombophilic families.

Why men appear to have an increased risk of recurrent venous thrombosis compared with women is unknown. In a cohort study of families with thrombophilia, lifetime risk of recurrent venous thrombosis was assessed in men and women (n = 816). Adjusted relative risk of recurrence was 1.6 (95% CI, 1.3-2.0) in men compared with women. Women were younger at time of their first event (mean, 34 years vs 44 years; P < .001) and at time of recurrence (40 years vs 48 years, P < .001). After excluding provoked first and recurrent venous thrombosis, adjusted relative risk was 1.2 (95% CI, 0.8-1.7), although mean age at recurrence was comparable in men and women (50 years vs 49 years, P = .595). In women with a hormonal first event, median interval between first event and recurrence was 10.4 years versus 2.7 years in men (P < .001). This difference was not observed when only unprovoked events were considered (P = .938). The difference in lifetime risk of recurrent venous thrombosis between men and women in thrombophilic families can be explained by a younger age of women at time of first venous thrombosis due to hormonal risk factors, and a longer interval between a provoked first episode of venous thrombosis and recurrence in women.