Background: Gestational Diabetes Mellitus (GDM) known as an intolerance for glucose that identified during pregnancy, it leads to many macroscopic and microscopic placental changes, thus are responsible for increases fetal perinatal illness and mortality. Thrombomodulin (TM) is a known indicator for the endothelial damage, when it is expresses as an essential substance of protein C anticoagulant system, that act like a receptor for thrombin to cease change of the fibrinogen to fibrin and activates the aggregation of platelet and thrombous formation