Natural evolution of thyrotropin and thyroid hormones concentrations in hypothyroid newborns with thyroid agenesis or ectopy during the first month of life.

Thyroid hormones and thyrotropin concentrations obtained by different screening programs at different times after birth were pooled to study their natural evolution in congenitally hypothyroid newborns with thyroid ectopy or agenesis. In filter paper blood spots, the T4 concentrations were higher in the group with thyroid ectopy whereas it was the opposite for the TSH values. Serum T4 decreased progressively in cases of thyroid agenesis. In ectopy, serum T4 remained stable after 2 weeks whereas the T3 concentration increased into the normal range. Thus, even at five weeks of age, the T4 levels of infants with ectopic thyroid are still in the hypothyroid range despite thyrotropin overstimulation.