Role of iodine supply in neonatal adaptation of the thyroid system

Abstract

Population frequency of neonatal hyperthyrotropinemia (NHT) in an iodine deficient region was studied with consideration for published reports about the relationship between prenatal iodine supply and fetal and neonatal thyroid function, and the efficiency of iodine prevention of this condition was evaluated by the results of overall screening of newborns for hypothyrosis. The concentrations of thyrotropic hormone (TTH) in whole blood specimens dried on paper were measured in 29588 newborns in the Belgorod region (Russia) in 1995-1998 using the Neonatal hTSH FEIA (Labsystems OY, Finland). Slight iodine deficiency in this region (median iodine excretion with urine 69 mcg/liter, n = 1313) was associated with an extremely high incidence of NHT: more than 5 iU/liter in 47% and more than 20 iU/liter in 7% newborns. Overall prevention with iodinated table salt during 1 year notably decreased the incidence of NHT (by 1.6 times, p < 0.001) and alleviated its severity from severe to mild degree. Preventive treatment of pregnant women by potassium iodide (200 mcg/day) during the same period more effectively decreased the incidence of the pathological parameter (five fold, p < 0.001). A lower incidence of NHT resultant from prenatal iodine treatment was associated with a lowering of the mean TTH level solely at the expense of the newborns with high levels of the hormone; if TTH levels were normal, they did not change. Therefore, thyroid dysfunction in newborns (NHT) indicates iodine deficiency in a region during intrauterine development; this abnormality can be prevented by iodine treatment in microdoses meeting the physiological requirement in iodine, which is increased during gestation. At the beginning of overall prevention of goiter by iodinated table salt, group prevention with potassium iodide is justified in risk groups, primarily in pregnant women; compensation of prenatal deficiency decreases the cost of screening for congenital hypothyrosis due to a lower requirement in TTH retesting.