Fetal hypothyroidism and maternal thyroid status in severe endemic goiter.

The relationship between maternal thyroid function and newborn thyroid function was studied in a region of very severe endemic goiter (Ubangi, Republic of Zaïre). T4, T3, and TSH concentrations were measured in the sera of 56 mothers (at the time of delivery) and 60 newborns (in the cord). The results obtained in these groups (untreated) were compared with those obtained in two control groups, comprising 53 mothers whose iodine deficiency had been corrected by the injection of iodized oil and 68 neonates born to such mothers. The results show that the mean (+/- SEM) T4 serum concentration (micrograms per dl) was 11.5 +/- 0.7 in the untreated mothers compared with 15.7 +/- 0.7 in the treated mothers (P less than 0.001), and 9.4 +/- 0.8 in the untreated newborns compared with 12.4 +/- 0.5 in the newborns of treated mothers (P less than 0.01). The values observed for the mean T3 serum concentrations (nanograms per dl) in the same groups were 171 +/- 10 and 154 +/- 9 (mothers; P greater than 0.05) and 68 +/- 6 and 55 +/- 6 (newborns; P greater than 0.05); the mean TSH serum concentrations (microunits per ml) were 8.7 (7.6 - 9.9) and 5.4 (4.9 - 5.9; mothers; P less than 0.001) and 19.6 (16.6 - 23.2) and 6.4 (5.8 - 7.0; newborns; P less than 0.001). The proportion of untreated newborns, i.e. 40%, with individual TSH values deviating by more than 2 SDS above the mean of the treated newborns is much greater than the corresponding proportion, i.e. 15%, of untreated mothers in relation to the treated ones. In 6 out of 34 untreated newborns, definite biochemical signs of congenital hypothyroidism were observed. Correlation coefficients were calculated between the untreated subjects. A positive correlation coefficient of 0.80 (P less than 0.001) was observed between the serum T4 concentrations of the mothers and those of the newborns, and one of 0.61 (P less than 0.001) was observed between their respective serum TSH values. Significant inverse correlations were observed between maternal serum T4 and cord serum TSH (-0.79; P less than 0.001) and between cord T4 concentrations and maternal TSH concentrations (-0.57; P less than 0.01). No definite trend is observed between the variations of serum T3 on one hand, and those of serum T4 or serum TSH on the other hand. Out of 51 mothers in whom serum T4 was determined, 11 showed values below 8 micrograms /dl; the newborns of those mothers showed very low serum T4 values (5.5 +/- 1.6 micrograms/100 ml) and extremely high serum TSH levels [144 (98-210) microU/ml]. It is concluded that, contrary to the situation observed in physiological conditions, maternal thyroid function in regions of severe endemic goiter is a good indicator of newborn thyroid function. The reasons for this probably lie in the influence of environmental factors acting simultaneously on the mother and the fetus.