Effects of labor and delivery on fibrinolysis

Because timing of sampling is crucial in an investigation of the effects of labor and delivery on fibrinolysis we conducted a study of fibrinolytic markers in plasma of 10 healthy multiparous women in whom labor was induced, which allowed standardization of sampling times in relation to the course of labor and delivery. Blood samples were taken 5 min before the start of oxytocin infusion, at full cervical dilatation, and within 5 min after delivery of the placenta. A sample of mixed free flowing cord blood was obtained after delivery with the placenta in situ. Variables determined were tissue-type plasminogen-activator (t-PA) and the plasminogen activator inhibitors type 1 (PAI-1) and type 2 (PAI-2). The only significant change between the beginning of the induction of labor and the end of the first stage of labor was a rise in t-PA antigen (P = 0.01). All variables, except PAI-2 antigen, changed significantly after delivery of the placenta: t-PA antigen and activity showed a rise (P < 0.05), accompanied by a fall in PAI-1 antigen and activity (P < 0.01). T-PA activity in cord plasma was higher (P < 0.01) in comparison with maternal plasma concentrations at the end of the first stage of labor, t-PA antigen levels were similar, and PAI-1 antigen and activity and PAI-2 antigen were lower in cord plasma (P < 0.001). Our study shows that activation of the maternal fibrinolytic system can already be detected during labor, with a marked further increase in fibrinolytic potential after placental separation.