Maternal thyroid hormone levels in pregnancy and the subsequent cognitive and motor performance of the children.

Serum levels of thyroxine and triiodothyronine during pregnancy were measured in women from a severely iodine deficient region in the highlands of Papua New Guinea. Subsequently the children born to these women were examined when aged 10-12 years and measures made of intellectual ability and motor competence. A significant correlation between these measures in the children and the maternal thyroxine but not maternal triiodothyronine level was observed. It is speculated that maternal thyroxine and not triiodothyronine may be essential for normal neurological maturation of the fetus before the fetal thyroid becomes functional.