Prospective study of exogenous hormones and risk of pulmonary embolism in women

Background. Current use of oral contraceptives (OCs) is a well-recognised risk factor for venous thrombosis and consequent pulmonary embolism (PE). Little is known about residual effects of past OC use. Furthermore, few epidemiological studies have assessed the relation between postmenopausal use of hormones and thrombotic disease. Methods. In this prospective study information was obtained through questionnaires sent every 2 years (1976-92) to 112 593 women aged 30-55 in 1976. We excluded women with previously diagnosed cardiovascular disease or cancer in 1976 and at the beginning of each subsequent 2-year follow-up period. Findings. From self-reports and medical records, we documented 123 cases of primary PE (no identified antecedent cancer, trauma, surgery, or immobilisation). Current users of postmenopausal hormones had an increased risk of primary PE (relative risk adjusted for multiple risk factors 2 .[95% Cl 1.2 - 3.81). However, past use showed no relation to PE (1.3 [0.7 - 2.4]). In current users of OCs the risk of primary PE was about twice that in non-users (2.2 [0.8 - 5.9]), but this finding was based on only five cases who were current OC users. Users of OCs in the past had no increase in risk of PE (0.8 [0.5 - 1.2]). These relations were consistent irrespective of cigarette-smoking status. Interpretation. Primary PE was uncommon in this cohort. The risk was increased by current though not past use of postmenopausal hormones or OCs.