In normal pregnancy extensive changes take place in the hemostatic system, involving in particular the coagulation and fibrinolytic systems. These physiological changes seem to have two major interrelated functions. First, to maintain the integrity of the expanding maternal and fetal circulations at the interface of the placenta and, secondly, to ensure the rapid and effective control of bleeding from the placental site during and after placental separation.

During normal childbirth profound changes in the fibrinolytic system take place. Tissue plasminogen activator (t-PA), the antigen and its biological activity and, the activity of plasminogen activator inhibitor (PAI): were measured in twenty-two healthy women during and shortly after spontaneous delivery (2nd stage and 3rd stage of labour, 48 and 72 hours post partum). Significant increases of plasma t-PA antigen and activity occurred during childbirth and before delivery of the placenta, while the inhibitor remained unchanged. After delivery the PA inhibitor and t-PA antigen showed a steep decline. The activity of t-PA remained largely unchanged during labour and after delivery. The comparison between the activity levels of PAI in infant cord blood and in maternal peripheral blood, taken simultaneously during the process of placental separation, showed significantly higher PAI activity in the mother. In contrast the levels of t-PA activity were found to be significantly higher in cord blood. Our results demonstrate that during the process of child-birth and separation of the placenta distinct alterations in the fibrinolytic system occur most likely due to placental effects.