3RD-GENERATION ORAL-CONTRACEPTIVES AND HERITABLE THROMBOPHILIA AS RISK-FACTORS OF NONFATAL VENOUS THROMBOEMBOLISM

Third generation oral contraceptives (OCs) are apparently stronger ris k factors for venous thromboembolism (VTE) than other OCs, however, th e increased risk may be due to confounding by indication related to di fferences in prescription behaviour. We estimated the risk of VTE asso ciated with use of OCs with and without the presence of Factor V Leide n mutation, protein C-, protein S- or antithrombin deficiency. Sixty-s even cases with VTE were compared with 134 controls. The risk of VTE i n the presence of thrombophilia was of the same magnitude for third ge neration OC users as for users of other OCs; OR: 52.5 (95% CI: 3.7-738 .1) and OR: 63.3 (95% CI: 6.2-618.4), respectively. It is unlikely tha t confounding by indication entirely explains the risk of VTE associat ed with third generation OCs since the combined effect exceeds what co uld be explained if this source of error was the only determinant of t he association.