Thrombin generation, D-dimer and protein S in uncomplicated pregnancy

Gestational age-specific reference values are essential for the accurate interpretation of haemostatic tests during pregnancy. Our 1-year prospective study included 40 healthy pregnant women with a median age of 30 (range 22–40) years; the subjects were followed in order to establish the gestational age dependent values for endogenous thrombin potential (ETP), D-dimer and protein S (activity and free). During the first trimester 50% of studied women had ETP >100% (reference values out of pregnancy); in the second trimester an ETP over 100% was observed in all women; ETP values remained unchanged during the third trimester. In the first trimester, the median D-dimer concentration of 0.30 mg/L, in the second 0.91 mg/L and in the third of 1.45 mg/L were observed. During the first trimester 14/40 subjects had protein S activity below reference range (