Among women taking oral contraceptives, shifts were observed in the balance between the generation of thrombin and its inactivation by amithrombin'III. These shifts were similar 10 those seen in patients with clinical thromboses unrelated to hormone therapy and were most severe in women who developed thrombovascular symptoms while taking oral contraceptives. These findings suggest that a small percentage of women may have a thrombotic predisposition associated with the use of these drugs and that the test systems may identify this predisposition in the same manner as they identify patients with clinical thromboses. They suggest further that women with cither sharply increased thrombin generation or severely depressed serum antithrombin-III activity maybe inappropriate candidates for further oral contraception.
(C) 1973 The American College of Obstetricians and Gynecologists