A simplified method for diagnosis of gestational age in the newborn infant.

concept that conversion of T4 to T~ depends upon a 5'monodeiodinase enzyme system that is immature at birth? The 3,3'T2 is thought to be derived at least in part from the peripheral conversion of T~ and reverse T~? In this infant, the 3,3'T~ level was high at birth, and remained elevated until the twenty-sixth day; therefore, it seems likely that the enzyme or enzymes capable of forming 3,3'T~ in thyrotoxicosis are operative at birth. LATS-P was present in high concentrations-i n the serum of both mother and infant, whereas LATS was measurable in both at low levels which could be considered nonspecific? The high concentration of LATS-P in the infant's serum when he was hyperthyroid and its reduction to undetectable levels when he became euthy-. roid suggest a role for this thyroid-stimulating immunoglobulin in the development of neonatal thyrotoxic0sis? Although the routine measurement, in all pregnant thyr0toxic women, of the thyroid-stimulating immunoglob.ulins LATS and LATS-P may be helpful in detecting neofmtal thyrotoxicosis, a definitive diagnosis of this disorder requires the demonstration of elevated iodothyronines in the infant. Although T4 and rT3 levels in cord serum are normally higher than in serum of euthyroid adults, ~" ~ markedly elevated levels should suggest hyperthyroidism. An elevated cord serum T3 value may be diagnostic, since it is normally very low, ~. s and an elevated cord serum 3,3'T: level also indicates overproduction of iodothyronines. This patient illustrates that a variety of iodothyronines are abnormally elevated in neonatal thyrotoxicosis, and supports the concept that the disorder is produced by transplacental transmission of thyroid-stimulating immunoglobulins.