Hyperprolactinaemia in congenital hypothyroidism.

Serum prolactin concentrations were measured in nine untreated hypothyroid infants and 23 euthyroid controls. In the former group the serum prolactin concentrations were tenfold higher than the controls (352 vs 34 micrograms/l), declining gradually upon treatment. Although serum prolactin concentrations can be mildly elevated in adults with hypothyroidism, congenital hypothyroidism causes a profound and probably uniform hyperprolactinaemia; furthermore, the hormone concentration correlates directly with the simultaneous TSH concentration. The physiological importance, if any, of the hyperprolactinaemia in the fetus or neonate is uncertain.