Hormonal contraception and risk of venous thromboembolism: national follow-up study

Objective To assess the risk of venous thrombosis in current users of different types of hormonal contraception, focusing on regimen, oestrogen dose, type of progestogen, and route of administration.Design National cohort study.Setting Denmark, 1995-2005.Participants Danish women aged 15-49 with no history of cardiovascular or malignant disease.Main outcome measures Adjusted rate ratios for all first time deep venous thrombosis, portal thrombosis, thrombosis of caval vein, thrombosis of renal vein, unspecified deep vein thrombosis, and pulmonary embolism during the study period.Results 10.4 million woman years were recorded, 3.3 million woman years in receipt of oral contraceptives. In total, 4213 venous thrombotic events were observed, 2045 in current users of oral contraceptives. The overall absolute risk of venous thrombosis per 10 000 woman years in non-users of oral contraceptives was 3.01 and in current users was 6.29. Compared with non-users of combined oral contraceptives the rate ratio of venous thrombembolism in current users decreased with duration of use (4 years 2.76, 2.53 to 3.02; P