IS RADIOIODINE (I-131) TERATOGENIC ?

Abstract

Use of radioiodine is absolutely contraindicated during pregnancy,¹ although dose to fetal thyroid is small, but sensitivity and untoward effect may be of medicolegal consequence. However, gonadal exposure is extremely low (less than a diagnostic radiograph), genetic effects are unlikely, extensive studies have failed to show I-131 related neoplasm or birth defects. ^{(2 to 7)}

No significant increase in genetic abnormalities has been documented in children of Japanese parents exposed to atomic radiation,⁸ and there is an increased tendency to treat young patients with I-131 in recent years.⁹ In human beings, organogenesis does not begin until the third week after conception. There is no evidence that radiation of a conceptus in the early weeks of pregnancy is more dangerous than irradiation of the ovary before fertilization. The International Commission on Radiological Protection (ICRP) withdrew support for the 10-day rule in 1984. Many agree that pregnancy be allowed to continue after known exposure of less than 10 centi-Gray (cGy), but some would reduce the upper limit to 5 cGy in the second trimester¹⁰ (1 cGy = 1 rad). We found a healthy daughter born to a woman who inadvertently received radioiodine therapy during early pregnancy, and would like to report considering its rarity.