THE ACCUMULATION OF RADIOACTIVE IODINE BY HUMAN FETAL THYROIDS*

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Abstract
Tracer doses of 500 microcuries of I131 were given to 9 euthyroid women 24 hours before therapeutic abortions were done. The fetuses ranged from 6.5 to 15 weeks of age. Their thyroids were dissected out and the I131 uptake determined in a Texas tank. Then the thyroids were fixed and radio-autographs were made from the tissue sections. One woman with thyro-toxicosis was treated inadvertantly in the 19th week of her gestation with 6100 microcuries of I131. She became euthyroid and delivered a normal baby. At one year of age it was in good health and had normal thyroid function. Human fetal thyroid has the ability to accumulate demonstrable amounts of I131 by the 12th week of gestation. It is a matter of conjecture whether this accumulation is great enough to preclude I131 therapy of maternal thyrotoxicosis.