Oral contraceptives and thrombosis

The debate on whether the so-called third-generation progestogens (desogestrel, gestodene, and norgestimate) are associated with a higher risk of venous thrombosis than the older, so-called second-generation progestogens (principally levonorgestrel and norethindrone) continues. Much of the debate focuses on finding alternative explanations for the observed relationship. Alternative explanations include a prescribing bias, in which women at greater risk of venous thromboembolism were preferentially prescribed newer preparations; a failure by researchers to adjust adequately for residual confounding by age; and a failure by researchers to allow adequately for confounding by the duration of use of oral contraceptives. None of these explanations have been accepted without dispute, and the debate will clearly continue. A possible biologic explanation for the observed relationship of higher thrombosis risk with use of third-generation preparations has been put forward by Rosing et al. from Maastricht, who developed a new way of measuring activated protein C (APC) resistance. They found that users of third-generation preparations have higher acquired APC resistance than users of second-generation products. This finding requires confirmation.