Why the study?
Do third generation oral contraceptives increase the risk of non-fatal venous thromboembolism compared to other oral contraceptives in individuals with and without heritable thrombophilia?
Do third generation oral contraceptives increase the risk of non-fatal venous thromboembolism compared to other oral contraceptives in individuals with and without heritable thrombophilia?
The increased risk of VTE associated with third-generation oral contraceptives is unlikely to be entirely explained by confounding by indication, as the risk remains highly elevated in the presence of heritable thrombophilia.
Answers are grounded in this paper and cite their sources.
Thrombophilia markedly elevates VTE risk across OC generations; leaves open whether third-generation agents add excess risk beyond thrombophilia.
Third generation oral contraceptives (OCs) are apparently stronger risk factors for venous thromboembolism (VTE) than other OCs, however, the increased risk may be due to confounding by indication related to differences in prescription behaviour. We estimated the risk of VTE associated with use of OCs with and without the presence of Factor V Leiden mutation, protein C-, protein S- or antithrombin deficiency. Sixty-seven cases with VTE were compared with 134 controls. The risk of VTE in the presence of thrombophilia was of the same magnitude for third generation OC users as for users of other OCs; OR: 52.5 (95% CI: 3.7-738.1) and OR: 63.3 (95% CI: 6.2-648.4), respectively. It is unlikely that confounding by indication entirely explains the risk of VTE associated with third generation OCs since the combined effect exceeds what could be explained if this source of error was the only determinant of the association.
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Andersen et al. (1998) studied this question.
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