Tissue plasminogen activator levels change with plasma fibrinogen concentrations during pregnancy

To investigate the relationship between coagulation activities and the fibrinolytic system during normal pregnancy, we measured the plasma concentrations of coagulation factors, antithrombin III (AT III), D-dimer, tissue plasminogen activator (tPA), total protein S (TPS), and plasminogen activator inhibitor type 1 (PAI-1) in 436 apparently healthy pregnant, postpartum, and nonpregnant women. There were no significant changes in AT III, TPS, and factor XI concentrations during pregnancy and puerperium. However, factor VII, VIII, IX, and XII activities increased gradually as pregnancy progressed, reached maximum values in the third trimester, and returned to nonpregnant levels by 5–8 weeks postpartum. Plasma D-dimer levels in the third trimester of pregnancy were 1.23±0.42 µg/ml, significantly higher than for the first trimester (0.34±0.16 µg/ml, P<0.01). The tPA antigen levels averaged 1.8-fold higher in the late third trimester than in the first trimester; the plasma fibrinogen concentrations averaged 1.6-fold higher in the late third trimester than in the first trimester. Compared to the peak values during pregnancy, tPA levels averaged 39.8% lower and plasma fibrinogen concentrations averaged 40.0% lower at 5–8 weeks postpartum. The tPA levels correlated strongly with the plasma fibrinogen concentrations (r=0.52, P<0.01). In short, this study shows that tPA levels change in parallel with plasma fibrinogen concentrations during and after normal pregnancy.