Formation of HCG in the human fetoplacental unit.

HCG and beta-HCG were determined in umbilical arterial and venous blood immediately after spontaneous term delivery. HCG and beta-HCG are present in higher concentrations in arterial than in venous umbilical cord blood. The data are consistent with the hypothesis that HCG and beta-HCG are produced in the fetal compartment of the human fetoplacental unit, with a larger contribution of the female fetus as compared with the male.