Thyrotropin response to thyrotropin-releasing hormone in fullterm, euthyroid and hypothyroid newborns.

The serum concentration of thyrotropin (TSH) and the TSH response following thyrotropin-releasing hormone (TRH) were studied in 16 euthyroid babies from 16 to 172 hours after birth and in 2 primary hypothyroid babies, 3 and 28 days of age. Serum-TSH was measured before an intravenous injection of 40 mug TRH and after 30 and 180 min. In the euthyroid babies increased basal levels of TSH were seen shortly after birth, followed by a pronounced decline. The extent of TSH increase after TRH could be correlated with the basal levels, and the relative increase was comparable to that which occurs in adults. In the hypothyroid babies very high basal levels of serum-TSH were seen, 125 and 400 muU/ml respectively, with no further increase following TRH stimulation. It was concluded that in euthyroid fullterm newborn, the relative response of serum-TSH to TRH was equal to that of adults, in spite of elevated thyroid hormone concentrations. In the hypothyroid newborn very high levels of serum-TSH were seen and a supplementary TRH-test seems without diagnostic value in congenital hypothyroidism.