Serum T4, T3, r-T3, TSH and Tg levels in cord blood and maternal circulation at the time of delivery.

The concentrations of T4, T3, r-T3, TSH and Tg were determined in parallel in maternal serum at the time of delivery and in cord blood. The serum T3 concentration in cord blood was significantly lower than that in the serum of the mother. However contrary to T3, r-T3 in cord serum was significantly higher than in maternal serum. Also, the level of TSH in cord blood was considerably higher than in maternal serum. The concentrations of total T4 in maternal and cord serum did not differ markedly, even though the values (mean and individual) were somewhat lower in the cord serum. The concentrations of Tg in cord and maternal serum varied widely, although the mean value for Tg in cord serum was somewhat higher than in maternal serum. No correlation was found between Tg concentration and TSH level in cord or maternal serum.