Serum growth-promoting activity measured as [3H]thymidine incorporation into human activated lymphocytes and serum transferrin levels in newborns and mothers.

Serum growth-promoting activity measured as [3H]thymidine incorporation into human activated lymphocytes and serum transferrin levels were measured during the perinatal period in newborns and mothers. Both thymidine activity (TA) and transferrin levels were significantly increased at the time of delivery in mothers compared to control women, and there was a progressive return to control levels in the first 5 postpartum days. A significant correlation was found between TA and placental weight. In the newborns, TA was low in cord blood after vaginal delivery but not in the cord blood from babies born by cesarean section. In premature newborns, TA was lower than in full term newborns. In all newborns during the first 24 postnatal hours, there was an increase in TA with levels rising above adult control values: levels in cord blood were positively correlated with birth weight but not with thymidine activity. These data afford complementary insights into the humoral controls of growth in newborn infants.