Development of thyroid gland volume during the first 3 months of life in breast-fed versus iodine-supplemented and iodine-free formula-fed infants.

The spontaneous development of thyroid gland volume (TGV) during the first 3 months of life was studied in entirely breast-fed infants (n = 21) and compared to those fed an iodine-supplemented formula (n = 19), an iodine-free formula (n = 5), or partially breast-fed in addition to an iodine-free (n = 4) or an iodine-supplemented formula (n = 16). The TGV of the infants and their mothers was determined sonographically in addition to their urinary iodine concentrations 5-7 days postpartum and 3 months later. In ten additional lactating mothers the breast milk concentrations of thyroid hormones and iodine were determined. It was shown that at 3 months of age an infant consuming about 1000 ml breast milk per day receives about 2 micrograms thyroid hormones and 55 micrograms iodine per day. At the end of their first week of life the infants showed a TGV between 0.28 and 1.5 ml (median 0.61 ml) and a urinary iodine concentration between 0.03 and 16.3 micrograms/dl (median 3.0 micrograms/dl). At 3 months of age the TGV of the breast-fed infants had decreased by a median of 0.24 ml (= -34%; median of percentage changes) whereas those fed a formula without iodine had increased by a median of 0.26 ml (= +50%; median of percentage changes). Those receiving an iodine-supplemented formula showed a TGV reduction of 0.14 ml (= +2%; median of percentage changes). The TGV development of the partially breast-fed infants lay between those being exclusively breast or formula fed.(ABSTRACT TRUNCATED AT 250 WORDS)