Ocs and risk of VTE in women with thrombophilic defects

April 1, 2007

Although women with hereditary deficiencies of protein S, protein C, or antithrombin are at high risk for venous thromboembolism (VTE) while using combined oral contraceptives (COCs) and tend to have VTE at a younger age than nondeficient women (mostly because of pregnancies), overall risk during their reproductive years is hardly affected by the use of the birth control method, according to the findings of a retrospective family cohort study conducted in the Netherlands.

Although women with hereditary deficiencies of protein S, protein C, or antithrombin are at high risk for venous thromboembolism (VTE) while using combined oral contraceptives (COCs) and tend to have VTE at a younger age than nondeficient women (mostly because of pregnancies), overall risk during their reproductive years is hardly affected by the use of the birth control method, according to the findings of a retrospective family cohort study conducted in the Netherlands.

The authors of the study calculated overall annual incidences of VTE to be 1.64% in deficient women and 0.18% in nondeficient women (adjusted relative risk 11.9; 95% CI, 3.9–36.2). Risk was comparable in deficient ever and never users of COCs (1.73% and 1.54%, respectively). Annual incidence of VTE during COC use was 4.62% in deficient women versus 0.48% in nondeficient women (RR 9.7%; 95% CI, 3.0–42.4).

Finally, the risk of VTE while using COCs dramatically increases in women who have more than one deficiency. As a result, the authors of the study recommend that COCs be strongly discouraged in women with inherited deficiencies of protein S, protein C, or antithrombin and perhaps even discouraged in nondeficient female relatives unless they have negative test results for all known thrombophilic defects.