Antithrombin III concentration in women using low-dosage progestogen for contraception

Abstract The concentrations of antithrombin III in serum and plasma, measured by the single radial immunodiffusion method, were significantly higher in women who used 0.5 mg. of chlormadinone acetate daily than in a comparable control group of women who did not take hormone-containing drugs. Very low concentrations of antithrombin III are associated with an increased risk of thromboembolic disease. Combined estrogen-progestogen pills have previously been shown to lower the antithrombin III concentrations moderately. Judged by this parameter, there is likely to be less risk of intravascular coagulation from low doses of chlormadinone.