Changes of hemostasis variables during pregnancy.

Normal pregnancy results in significant changes in maternal plasma coagulation factors, elements of the protein C/protein S natural anticoagulant system, and markers of fibrinolysis. These changes result in an increase in thrombin and fibrin generation, which is necessary for the hemostatic challenge of delivery and for normal placental implantation and development. In this review, the evidence for these changes in both the antenatal and peripartum period is discussed. An understanding of these physiological changes is required to allow a diagnosis of inherited or acquired thrombophilic or bleeding disorders during pregnancy and may give insight into the development of the thrombosis-linked disorders associated with pregnancy.