Do lowered factor VII levels at extremely high endogenous oestradiol levels protect against thrombin formation?

The purpose of the study was to find a model to study the effect of endogenous oestradiol on haemostasis. Hormones and haemostatic variables were therefore measured before and after in vitro fertilization and egg replacement therapy in 14 women with tubal infertility. The differences between the levels of the haemostatic variables at minimum and maximum levels of oestradiol and progesterone were evaluated. A significant increase in the plasma levels of coagulation factor VIII, von Willebrand factor and fibrinogen was found between samples drawn before stimulation and at the highest oestradiol levels (P < 0.002, P < 0.002 and P < 0.015, respectively). However, coagulation factor VII activity and antigen decreased significantly (P < 0.001 and P = 0.009, respectively). The levels of the coagulation inhibitors protein C and antithrombin decreased (P < 0.003 and P = 0.008, respectively), while that of free protein S increased (P = 0.039). No significant changes were observed in the fibrinolytic variables or in those reflecting thrombin activity (prothrombin fragment 1 + 2, thrombin-antithrombin complexes, soluble fibrin and D-dimers). In conclusion, the increase in the levels of factor VIII, von Willebrand factor, fibrinogen and the decrease in the levels of antithrombin and protein C may, if coagulation is triggered, contribute to a hypercoagulable state. The depressed factor VII levels and the tendency to elevated free protein S levels may constitute a protective mechanism that modulates the coagulation system when levels of oestradiol become extremely high.