Risk of recurrent venous thromboembolism among young women after a first event while exposed to combined oral contraception versus not exposed to: a cohort study.

The risk of recurrent venous thromboembolism (VTE) in young women after a first oestrogen contraception associated VTE episode is unknown. This uncertainty has an impact on the decision whether to stop anticoagulant treatment. Our objective was to assess the risk of recurrent VTE in women after a first VTE episode on oestrogen contraception. This was a prospective cohort study in which we consecutively enrolled between 1992 and 2011 all women under 50years with a first objectively confirmed VTE. The incidence of recurrent VTE during follow-up after stopping anticoagulation was compared between women users and non-users of combined oral contraception (COC) at the time of index VTE. Of the 241 women aged 50 or younger seen for a first VTE and followed-up after stopping anticoagulation, there were 180 COC-users and 61 non-users. Median duration of follow-up off-anticoagulants was 66 months (interquartile range: 33-103). There were 14 recurrences in COC-users and 5 cases in non-users. No significant association was found between exposure to COC and the incidence of recurrent VTE after adjustment for age or after restricting the analysis to major unprovoked VTE: incidence rate of recurrence 17.9/1,000/year (95% CI: 9.6-33.2) in women with COC as compared with 17.6/1,000/year (95% CI: 6.6-47) with an incidence ratio of 0.7 (95% CI: 0.2-2.4, p=0.59). The risk of recurrent VTE is low in young women after a first VTE. However, this risk is not significantly lower in women after a first VTE while exposed to combined oral contraception.