Re: Declared Pregnant Worker Question

[westbrookjl@ornl.gov (Janet L. Westbrook)]

To Greg Krause:

I dug into my binder of information about radiation and the fetus and found
the following, for your information. It is from Dr. Brent's excellent and
comprehensive chapter from the reference below. Although he is speaking
about medical administrations, obviously his remarks are applicable to an
inadvertent uptake situation as well.

Please note that if an actual case of uptake were to occur, you would be
best advised to consult an expert in assessing the effects on the fetus. I
expect that in the case of your worker, the uptake and thus the dose to the
fetus would be small. But again, the peace-of-mind factor is important.

							Janet Westbrook


Brent states that "The fetal thyroid absorbs and incorporates iodides
readily by the tenth week of gestation and continues to do so thereafter.
Fetal thyroid avidity for iodides is greater than maternal thyroid
activity....Even in the case of bound iodides that do not cross the
placenta, in time a substantial amount of iodide released from the binding
molecule becomes available to the fetus...Although there are no reports of
immediate deleterious effects from tracer doses of radioactive iodine, a
theoretic concern about the induction of thyroid cancer cannot be
disregarded....Even if administered during the first 5 or 6 weeks of human
gestation, when the fetal thyroid has not yet developed, the total dose to
the embryo should be estimated. Ordinarily, the whole-body dose to the
embryo from I-131 is insignificant when compared with the thyroid dose,
because the whole-body dose is primarily due to gamma irradiation, whereas
the thyroid dose is due to beta particles as well as gamma rays emitted
from iodides concentrated in the thyroid tissue. But if large doses of
I-131 are administered, significant embryonic or fetal exposure can occur
because of the accumulation of I-131 in the [maternal] bladder adjacent to
the uterus". Brent also quotes S. Goldman (see reference below) as follows
for the thyroidal radioiodine dose to the fetus: "10-12 weeks, .001 rad per
uCi ingested by the mother; 12-13 weeks, .7 rad/uCi; 2nd trimester, .7
rad/uCi; just before birth, 8 rad/uCi".

Brent, R. L., "The Effect of Embryonic and Fetal Exposure to X Rays,
Microwaves, Ultrasound, Magnetic Resonance, and Isotopes", in Medical
Disorders During Pregnancy, Second Edition, Barron and Lindheimer, eds., 1994

Goldman, M., Health Physics, 29:874, 1975



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