In order to elucidate the mechanisms responsible for the high frequency of transient hypothyroidism observed in premature infants in Belgium, we conducted morphological and biochemical studies of thyroid glands collected immediately after death in 14 premature infants (gestational ages 25–35 weeks) who died less than 12 days after birth and compared the results with those obtained in normal adults and in adults with iodine poor non-toxic colloid goiter. The thyroid glands of the prematures exhibited morphological characteristics of hyperstimulation and their serum levels of TSH at the time of death were markedly elevated (27.1±4.5(SEM) μU/ml). In the prematures and in the adults with colloid goiter as compared to normal adults, the concentrations of intrathyroidal iodine, MIT, DIT, and T4 were markedly reduced. In the glands of prematures, the MIT/DIT and T3/T4 ratios were normal but, as compared to adults with colloid goiter, the concentrations of thyroglobulin and the fraction of organified iodine were markedly reduced. These two factors result in an unsufficient utilization of the available iodine, which partly accounts for the very low iodine content of the thyroids observed in the Belgian prematures (20 to 100 μg v. 10,000 to 20,000 in normal adults). In our country this reduction of the thyroidal pool of iodine could be aggravated by the low dietary supply of iodine and play a decisive role in the development of transient hypothyroidism in prematures.
展开▼
