Roles of serum thyroxine-binding proteins and maternal thyroid hormones in fetal development.

Endocrinologists have speculated for many years about three apparently unrelated topics--the unknown physiological role of specific thyroid (and steroid) hormone-binding proteins present in serum; the extent and significance of placental transport of thyroid hormones from mother to fetus throughout pregnancy; and the specific hormonal role (if any) of thyroxine. A unifying hypothesis is advanced for the existence of subtle endocrine control systems which may profoundly affect early fetal development and ultimate intellectual and behavioural attainments in adults.