Hemostatic changes in pregnancy

Abstract

Normal pregnancy is associated with changes in all aspects of haemostasis, including increase in concentrations of most clotting factors, decreasing concentrations of some of the natural anticoagulants and diminishing fibrinolytic activity. These changes help in maintaining placental function during pregnancy but result in a state of hypercoagulability that may predispose to thrombosis and placental vascular complications. During pregnancy, the concentrations of coagulation factors V, VII, VIII, IX, X, XII and von Willebrand factor rise significantly, accompanied by a pronounced increase in fibrinogen levels which increases up to two-fold from non-pregnant levels. Furthermore, there is a decrease in physiological anticoagulants manifested by a significant reduction in protein S activity and by acquired activated protein C resistance. The overall fibrinolytic activity is impaired during pregnancy, but returns rapidly to normal following delivery. This is largely due to placental derived plasminogen activator inhibitor type 2 (PAI-2), which is present in substantial quantities during pregnancy. D-Dimer levels increase in pregnancy but are not thought to indicate intravascular coagulation as fibrinolysis is depressed. These D-Dimers may originate from the uterus. Finally, the platelet count decreases in normal pregnancy possibly due to increased destruction and haemodilution with a maximal decrease in the third trimester. Immediately after delivery there is an increase in platelet count, especially in patients undergoing cesarean section. During treatment of severe post-partum hemorrhage, it is absolutely essential to have the knowledge that the starting values of the platelets are very different as compared to a non-pregnant patient. Moreover, after delivery, also the levels of fibrinogen increase. Since the value of fibrinogen represents a crucial parameter for the management of acute bleeding, it is essential to administer the proper amount of fibrinogen in the case of postpartum hemorrhage. This aspect is emphasized especially in relation to the use of thromboelastography and for a correct interpretation of the results. Thromboelastogram profiles strongly depend on the amount of platelets and fibrinogen in whole blood. Protocols for thromboelastogram guided administration of hemocomponents and coagulation factor concentrates in cases of acute bleeding in pregnancy and post-partum are required.