[Placental permeability to thyroxine]

This is an experimental work. Investigations were carried out on albino rats on the 18th day of pregnancy. A study was made of I-131-labelled thyroxin penetration from the maternal organism into the fetus and vice versa. Radiological and radiochromatographic analysis of the blood samples of both the mother and the fetuses at various time intervals after the administration of radioactive thyroxin showed that the isotope in the form of thyroxin failed to penetrate from the mother to the fetus and vice versa. A conclusion was drawn that during prenatal development the function of the fetal thyroid gland was automatic.