Summary

Changes in the coagulation and fibrinolytic systems during pregnancylead to a higher risk of thromboembolism.These changesinclude the increase of many clotting factors, as well as a significantfall in activity of fibrinolytic proteins,such as protein C.ProteinZ is a vitamin-K-dependent plasma glycoprotein and inhibitsthe activation of factor X by serving as a cofactor to a plasmaproteinase inhibitor. Protein Z deficiency has recently been reportedin women with unexplained early fetal losses, and antibodiesto protein Z can contribute to adverse pregnancy outcomes.The aim of this study was to determine the range of proteinZ in normal pregnancies at different gestational weeks in a cross-sectional and a longitudinal setting. In the longitudinalstudy we found a 20% increase (p=0.006) of protein Z from firsttrimester to delivery and a 30% decrease (p<0.0001) 6 to 12weeks after delivery. In the cross-sectional study these findingswere reproducible. In summary, our data show a progressive increasein protein Z levels with gestational age in normal pregnanciesand a return to normal levels around 6 to 12 weekspostpartum.The normal increase of protein Z during pregnancymay balance the increase of clotting factors to protect pregnantwomen from thrombosis.