Oestrogen and thyroxine-binding globulin levels in early normal pregnancy

Peripheral serum levels of thyroxine-binding globulin (TBG), unconjugated and total oestrone, and unconjugated oestradiol-17 beta were measured twice in 60 cases of early normal pregnancy (gestational weeks 6-19). Although highly significant correlations between TBG and oestrogen levels were obtained in the total material, the correlations within two-week intervals of pregnancy were rather poor and mostly insignificant. Furthermore, there were no associations at all between the increase rates of TBG and those of the oestrogens, either within two-week intervals or in the total material. The findings do not support the common concept of continuously rising oestrogen stimulation as the main factor affecting the TBG synthesis during pregnancy.