[Blood levels of molecular variants of human thyroxine-binding globulin].

The concentrations of the molecular variant of the thyroxine-binding globulin (TBG-1) and total TBG were measured in normal human sera (male and female), venous blood sera at various stages of normal pregnancy as well as in matched samples of retroplacental and venous sera of mothers and in cord sera of their newborns. It was shown that TBG-1 appeared on the 6th-11th week of pregnancy and its level increased up to the delivery. A TBG-1 portion in the total TBG content increased from 2.0% in the 3rd month of pregnancy to 8.8% in the last month. After delivery TBG-1 and TBG levels decreased on the first day from 3.82 +/- 0.52 micrograms/ml to 2.52 +/- 0.86 micrograms/ml (P less than 0.01) and from 43.3 +/- 7.2 micrograms/ml to 37.8 +/- 9.6 micrograms/ml (P less than 0.01), respectively. However on the 5th day a decrease in TBG-1 and TBG concentrations were not observed. TBG-1 was undetectable in normal adult and cord sera. TBG-1 concentrations in matched retroplacental and venous sera at term were similar. These results suggested that TBG-1 was related to pregnancy-associated proteins rather than to proteins of fetal or placental origin.