Corticosteroid-binding globulin and estrogens in maternal and cord blood.

Corticosteroid-binding globulin (CBG) is produced by the liver in small concentrations and binds steroids with high affinity. Its concentration in the blood is sensitive to endogenous or exogenous estrogens in a dose-response manner and serves as a biological assay for estrogens. CBG concentrations were measured in sera collected from maternal and umbilical vein blood during labor and delivery and at elective cesarean section and correlated with endogenous estradiol and estriol concentrations. CBG and estradiol concentrations of maternal blood were significantly exceeded those of maternal serum. A highly significant increase in cord blood estriol concentration was found following vaginal delivery compared to elective cesarean section, indicating an increase in adrenal activity due to the stress of labor. CBG levels correlated directly with maternal estradiol but not estriol cencentrations. Cord blood CBG concentration varied little despite a wide range of estrogen concentrations. The physiologic significance of CBG concentrations in maternal and fetal blood is discussed.