Effective Method for Prediction of Transient Hypothyroidism in Neonates Born to Mothers with Chronic Thyroiditis

ABSTRACT

An effective method of prediction of neonatal transient hypothyroidism was examined in 105 neonates (including a pair of twins) born to mothers with chronic thyroiditis (92 mothers with goitrous Hashimoto's disease and 12 with primary atrophic hypothyroidism). Antithyroid microsomal antibody was measured by a hemagglutination technique (MCHA), and antithyroid-stimulating hormone (TSH) receptor antibody by both radioreceptor assay (TBII) and biologic thyroid-stimulation blocking assay (TSBAb). For generalization of predictive criteria, the expression of TBII activity was standardized using standard serum made taking units of MRC-LATS-standard B as a reference, and that of TSBAb activity was standardized as the degree of dilution with normal pooled serum to attain 50% inhibition of TSH (100 μU/ml)-induced cyclic adenosine monophosphate increase (TSBAb₅₀). The MCHA titer in maternal serum at delivery correlated well with that of the corresponding cord serum, butnotwith the free thyroxine (T₄) index or the TSH level in cord serum. TBII activity was positive in only 4 of 12 mothers with primary atrophic hypothyroidism, TSBAb activity was also positive only in these four mothers, and neonatal thyroid dysfunction was observed in three of their neonates. Two of these neonates developed transient hypothyroidism requiring T₄ treatment, and the third developed mild transient hyperthyrotropinemia with normal T₄ and triidothyronine levels. The mothers whose neonates showed transient hypothyroidism had TBII activities of more than 300 U/ml and TSBAb₅₀ activities of more than 300. Ninety-two mothers with goitrous Hashimoto's disease had neither TBII nor TSBAb activity, irrespective of their thyroid function, and delivered euthyroid babies. These data indicate that the MCHA titer has no effect on neonatal thyroid function. For effective prediction of neonatal transient hypothyroidism, TBII needs to be measured only in patients with primary atrophic hypothyroidism, and neonatal transient hypothyroidism can be predicted when the maternal TBII activity is strongly positive (more than 300 U/ml). TSBAb₅₀ activities of more than 300 provide support for the prediction.