Fetal CNS Effects

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    Approximately after the eighth to tenth week post-conception, organogenesis in the fetus begins and organ systems start to form.
    The fetal thyroid can begin to accumulate iodine at about 10 weeks gestational age.
    A high fetal thyroid dose from radioiodine can result in permanent hypothyroidism.
    If pregnancy is discovered within twelve hours of radioiodine administration, prompt oral administration of stable potassium iodine (60-130 mg) to the mother can reduce fetal thyroid dose.
    This may need to be repeated several times to ensure fetal exposure is minimized.
    Remember that the ALI for Iodine-131 is only 30 uCi to an adult person to receive a 50 rem thyroid exposure. This is why most nuclear medicine clinics perform pregnancy tests before administering any radioiodines to women of child bearing age.
    These effects were seen in the fetuses of atomic bomb survivors and children exposed in utero after Chernobyl.


Page 113

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