Thrombotic risk factors and oral contraception.

Eighty-one women with a history of thrombosis were classified into three groups: group I (n = 29), women in whom thrombosis developed during oral contraception; group II (n = 33), those who used oral contraceptives (OC) without complications but experienced vascular occlusion in other risk situations; group III (n = 19), women who never used OC. The level of antibodies to anionic phospholipids (PLa), a response to activated protein C (APC), and the presence for the mutation in the coagulation factor V gene causing APC resistance were studied. In the studied groups, APC resistance was present in 14% to 42% of patients. PLa were elevated in about half of APC-resistant patients. The incidence of APC resistance correlated with the recurrency of the thrombotic events within the groups. In most cases it was tightly connected to the mutation in the factor V gene. Women in whom thrombosis developed while they were taking OC (group I) differed from the others, having a remarkable disagreement between the lowest incidence of APC resistance and a relatively increased number of the mutation (14% vs 38%, p < 0.025). This finding suggested that the APC response is flexible. An influence of OC that predisposes a reduction in APC response is discussed.