Thyroid function: fetal-maternal relationship at term.

The present study was undertaken to examine serum parameters of thyroid function at term in normal pregnant women and their normal fetuses. Paired sera from 56 mothers and their respective newborn infants' umbilical cord were obtained at parturition. Maternal and fetal TSH, FT4, T4, FT3 and T3 levels were measured and the differences between these two groups were analysed. The levels of fetal serum TSH (8.86 +/- 5.82 IU/ml) were significantly higher than maternal TSH levels (3.32 +/- 3.3 IU/ml) (P < 0.001), but there was no significant difference between the fetal and maternal T4, FT4 and T3. On the other hand, cord FT3 levels (1.7 +/- 1.2 pg/dl) were significantly lower than maternal levels (2.7 +/- 1.4 pg/dl) (P < 0.001).