A negative iodine balance is found in healthy neonates compared with neonates with thyroid agenesis

We studied the effects of the presence or absence of the thyroid gland on t he iodine metabolism and excretion in term Dutch newborns by performing a r etrospective study of the urinary iodine excretion in 193 term newborns wit h abnormal congenital hypothyroidism screening results. Thirty-six euthyroi d newborns with decreased thyroxine-binding globulin levels were compared w ith 157 hypothyroid patients, 54 due to thyroid agenesis and 103 due to thy roid dysgenesis. A significant difference in the urinary iodine excretion w as observed between the agenesis group (mean: 28 mu g/24 h) and the euthyro id newborns (mean: 46 mu g/24 h, P=0.001). In conclusion, healthy, euthyroid, term newborns excreted more iodine in th eir urine than newborns with thyroid agenesis. These results strongly indic ated the existence of a temporarily negative iodine balance: the excretion of iodine prevailed over the intake and the newborn's thyroidal iodine, sto red during pregnancy, could be used for thyroxine synthesis in the postnata l period. Since healthy term. neonates were able to maintain adequate plasm a free thyroxine concentrations under normal TSH stimulation, the prenatall y acquired iodine stores could be considered sufficiently high to compensat e for the transient postnatal losses.