Vitamin K dependent proteins in fetal hemostasis at mid trimester of pregnancy.

The vitamin K dependent coagulation factor activities were measured in 63 normal human fetuses from 19 to 28 weeks of pregnancy. These activities were included between 9 to 28 percent of normal adult levels. Prothrombin antigen, factor IX antigen and protein C were also measured. There is a good correlation between prothrombin procoagulant activity and antigenicity, suggesting that low level of these vitamin K dependent proteins in fetuses is probably a consequence of liver immaturity.