THYROTROPIN IN PLACENTA AND FETUS

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Abstract
Extremely minute quantities of placental TSH could invariably be detected in placental tissue whether it was spontaneously delivered or removed at the time of cesarian section. Blood TSH levels of pregnant women were far higher than those of normal male or female adults. The quantity of TSH in the pituitary of the pregnant rat was higher than in the non-pregnant, while gonado-tropin was lesser in amount during the period of gestation than in the non-pregnant period. Hence, an assumption is made that the higher blood TSH level of pregnant women implies hypersecretion of TSH from the anterior pituitary. The human fetal thyroid gland is filled with a colloidal substance early in the 4th month of gestation, and by the 8th month it develops lobes. The glandular organ structure is morphologically complete by the time of birth. The fact that we have failed to observe histological differences between fetal thyroid glands of pregnant rats administered a TSH product and a group of animals without such a drug seems to substantiate the interpretation that no TSH is transmitted across the placenta. Human fetal TSH in the pituitary could be estimated as soon as 12th week of gestation is past, and that the thyroid lobules are formed by the 23rd week of gestation at which time the TSH content increases rapidly with simultaneous appearance of PAS positive granules. Development of the fetal thyroid, therefore takes place solely under control of fetal TSH.