Fibrinolytic Inhibitors in Human Retroplacental Blood

Fibrinolytic inhibitors of plasminogen activation (urokinase inhibitors) and of plasmin (alpha2‐macroglobulin, antiplasmin and total antitrypsin activity) were measured in retroplacental blood and compared with that in placental extract and maternal venous blood obtained at 40 deliveries. In placental extract the concentration of inhibitors of plasminogen activation was extremely high. In contrast, it was found to be normal in retroplacental blood and close to the value found for maternal venous blood. It therefore seems unlikely that inhibitors from the placenta enter the bloodstream and contribute to the reduction of the fibrinolytic activity in the maternal circulation during pregnancy.