In vitro fertilization. Do short-term changes in estrogen levels produce increased fibrinolysis?

High estrogen levels have been implicated as a cause of thrombosis. Patients undergoing in vitro fertilization (IVF) present an opportunity to study isolated estrogen effects on the coagulation system, since hormonal manipulation is used to achieve varying estrogen concentrations. We evaluated the effect of estrogen levels on the fibrinolytic and clotting systems of 32 patients undergoing IVF from whom venous samples were obtained during a period of several weeks at baseline and retrieval times. Flow cytometric studies were performed to assay platelet activation. Hemostasis markers measured thrombin-antithrombin complexes (TAT), fibrinogen, plasmin-alpha 2-antiplasmin complexes (PAP), plasminogen activator inhibitor (PAI-1), and D-dimer. A significant decrease in PAI-1 and an increase in PAP were observed at high estrogen levels, suggesting an increase in fibrinolytic potential. However, the products of fibrinolysis, as measured by D-dimer levels, decreased at high estrogen levels. No changes were seen in platelet activation indicators or TAT levels. The fact that a decrease in products of fibrinolysis was seen at high estrogen levels despite concurrent changes in PAI-1 and PAP that normally accompany increased fibrinolysis may be due to alterations in the overall balance of the fibrinolytic system or to a delay in onset of fibrinolysis.