The overall absolute risk of venous thrombosis per 100,000 woman-years in current use of combined oral contraceptives is approximately 60, compared with 30 in non-users. The risk of thromboembolism varies with different types of birth control pills; compared with combined oral contraceptives containing levonorgestrel (LNG), and with the same dose of estrogen and duration of use, the rate ratio of deep venous thrombosis for combined oral contraceptives with norethisterone is 0.98, with norgestimate 1.19, with desogestrel (DSG) 1.82, with gestodene 1.86, with drospirenone (DRSP) 1.64, and with cyproterone acetate 1.88. In comparison, venous thromboembolism occurs in 100–200 per 100.000 pregnant women every year.