Maturation of foetal thyroid hormone synthesis and regulation

ABSTRACT

A total of 343 pairs of maternal serum and foetal cord serum samples were assayed for thyroxine (T4), triiodothyronine (T3) and thyrotropin (TSH) levels. Foetal serum total T4 levels showed a positive correlation not only with gestational age(r=0.14) but also with maternal serum T4 levels (r=0.42). Although these correlations were not very strong, they were statistically significant. Foetuses were found to be T3 deficient for all gestational age groups in the study. Despite these deficient levels, there was still a significant positive correlation between foetal serum T3 levels and the maternal serum T3 levels (r=0.24). Foetal serum TSH levels were about three times higher than the corresponding maternal levels for all gestational age groups. High TSH levels in the face of deficient T3 levels for all gestational age groups in the study indicated that the function of the foetal hypothalamic-pituitary feedback control system of the thyroid gland has been well established even before the foetal maturity.