Resistance to activated protein C as a basis for venous thromboembolism associated with pregnancy and oral contraceptives

OBJECTIVE: Inherited resistance to activated protein C, which is caused by a single factor V gene mutation, is a frequent risk factor for thrombosis. The purpose of this study was to determine the prevalence of activated protein C resistance in women with thromboembolic complications that had occured in connection with pregnancy or use of oral contraceptives. STUDY DESIGN: Activated protein C resistance was analyzed in women with previous thromboembolic complications in connection with pregnancy (n = 34) or oral contraceptives (n = 28), in healthy fertile women (n = 57), and in women during normal pregnancy (n = 18). Results of the activated protein C resistance test were expressed as activated protein C ratios, values <2 indicating activated protein C resistance. RESULTS: Activated protein C resistance was found in almost 60% of women with thromboembolic complications during pregnancy and in around 30% of women with thromboembolic complications during treatment with oral contraceptives. In nonpregnant controls approximately 10% had activated protein C resistance. In normal pregnancy activated protein C ratios were similar to those of normal controls. CONCLUSIONS: Activated protein C resistance, which is caused by a genetic defect in the factor V gene, was found to be highly prevalent in women with a history of thromboembolic complications during pregnancy. The gene defect is common in the general population, and the results evoke the question whether it would be reasonable to perform general screening for activated protein C resistance early during pregnancy or before prescription of oral contraceptives.