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THE recent implementation of screening programs for the detection of congenital hypothyroidism has focused attention on the unique thyroid physiology and pathophysiology of the newborn. A high prevalence of both permanent and transient disorders of thyroid function has been observed. In the following discussion we review recent information regarding development of the normal thyroid system in relation to the several permanent and transient abnormalities now recognized in the neonatal period.Normal Development of the ThyroidEarly OntogenesisThe fetal hypothalamic-pituitary thyroid system develops free of maternal influence: the mammalian placenta is impermeable to the natural iodothyronines, T4, T . . .
Fisher et al. (Thu,) studied this question.