Fibrinolytic activity in amniotic fluid during late pregnancy.

Fibrinolytic activity (FA) was assessed by the fibrin plate technique in 47 amniotic fluid samples obtained at 35 to 39 weeks' gestation. In amniotic fluid the FA (63.1 +/- 2.5 mm2) was considerably elevated when compared with previously reported serum levels of pregnant women. After centrifugation of the amniotic fluid samples a highly significant reduction of FA in the supernatant was recorded (42.9 +/- 1.3 mm2), suggesting that the cells of fetal origin are the main source of the high plasminogen activator activity demonstrated in amniotic fluid. A significant rise in amniotic fluid FA was demonstrated beyond the 37th gestational week. Furthermore, significantly greater FA was recorded in amniotic fluid samples from women with spontaneous onset of labor within a week. However, a single FA determination in amniotic fluid obtained by routine amniocentesis was found to be of little value for prediction of the time interval to delivery.