Norris L A, Bonnar J
Department of Obstetrics and Gynaecology, St James's Hospital, Dublin, Ireland.
Baillieres Clin Obstet Gynaecol. 1997 Sep;11(3):545-64. doi: 10.1016/s0950-3552(97)80027-2.
Oral contraceptives have been linked to an increased incidence of thrombovascular disease. This may be mediated by their effects on the haemostatic system. An increase in the activity of coagulation Factors VII, X and fibrinogen occur with pill usage. Increased Factor VII levels are dependent on both the oestrogen and progestogen component of the oral contraceptive. A reduction in antithrombin III levels has also been observed in some but not all studies. Increased fibrinolysis has also been shown in oral contraceptive users which should balance the changes in the coagulation pathway. The increase in fibrinolytic potential is thought to be due to a decrease in the levels of plasminogen activator inhibitor I combined with an increase in the levels of plasminogen; tissue plasminogen activator antigen is decreased in most studies. The increased levels of endpoints of coagulation and fibrinolysis in pill users indicate that enhanced activity of both systems is occurring in vivo. The increased coagulation activity appears to be balanced by the rise in fibrinolytic activity, so preserving haemostatic balance. Enhanced platelet activity has also been shown in women taking oral contraceptives. Thrombus formation can result, however, when local vascular wall damage exists, or when other risk factors for thrombo-embolism, such as older age and smoking, coexist and create a local activation resulting in a thrombus. In these situations, the small differences in levels of coagulation factors in women taking different oral contraceptive formulations may be important. Pills containing the lowest doses of oestrogen (20 micrograms ethinyloestradiol) have shown the least changes in haemostatic factors. The progestogen component of the pill modifies the effect of oestrogen on the haemostatic system.
口服避孕药与血栓性血管疾病发病率的增加有关。这可能是由其对止血系统的作用介导的。服用避孕药时，凝血因子VII、X和纤维蛋白原的活性会增加。因子VII水平的升高取决于口服避孕药的雌激素和孕激素成分。在一些但并非所有研究中也观察到抗凝血酶III水平的降低。口服避孕药使用者的纤维蛋白溶解也有所增加，这应该可以平衡凝血途径的变化。纤维蛋白溶解潜能的增加被认为是由于纤溶酶原激活物抑制剂I水平的降低与纤溶酶原水平的增加相结合；在大多数研究中，组织纤溶酶原激活物抗原减少。服用避孕药者凝血和纤维蛋白溶解终点水平的升高表明这两个系统在体内的活性增强。凝血活性的增加似乎被纤维蛋白溶解活性的升高所平衡，从而保持止血平衡。服用口服避孕药的女性也表现出血小板活性增强。然而，当存在局部血管壁损伤时，或者当存在其他血栓栓塞风险因素，如年龄较大和吸烟，并且共同导致局部激活从而形成血栓时，就会形成血栓。在这些情况下，服用不同口服避孕药配方的女性凝血因子水平的微小差异可能很重要。含最低剂量雌激素（20微克乙炔雌二醇）的避孕药对止血因子的影响最小。避孕药的孕激素成分会改变雌激素对止血系统的作用。
