Increased thrombin generation in normal pregnancy.

The aim of this longitudinal study was to evaluate whether an increased thrombin generation takes place in normal pregnancy by determining fibronopeptide A plasma concentration in 24 women at three stages of gestation. The activity of the main blood clotting inhibitors, antithrombin III and protein C., and platelet agregability were also investigated. Our study showed a significant rise of fibrinopeptide A plasma levels already manifest at the first trimester. Antithrombin III activity was found to slightly but significantly decrease during pregnancy, whereas protein C levels showed a moderate, significant increase. A slight platelet activation was observed in the second and third trimester. These findings indicate that during pregnancy a new equilibrium of blood clotting system arises, shifted to a hypercoagulable state which leads to the increased risk of thromboembolism observed in pregnancy.