Pregnancy after high therapeutic doses of iodine-131 in differentiated thyroid cancer: potential risks and recommendations.

Seventy female patients who had been treated with high doses of iodine-131 for differentiated thyroid cancer (DTC) and who had a subsequent pregnancy were evaluated. The total 131I dose ranged from 1.85 to 16.55 GBq (mean +/- SD = 4.39 +/- 25.20 GBq). Age at first therapy ranged from 15 to 36 years (mean +/- SD = 24.3 +/- 5.0 years) and the interval from 131I therapy to pregnancy varied from 2 to 10 years (mean +/- SD = 5.3 +/- 2.8 years). The estimated radiation dose to the gonads ranged from 10 to 63 cGy (mean +/- SD = 24.0 +/- 13.5 cGy). All patients were treated with L-thyroxine at doses capable of suppressing thyroid-stimulating hormone. Seventy-three children were followed-up and seven pregnancies are still in progress. One child was affected by Fallot's trilogy and three had a low birth weight through with subsequent normal growth; the others were healthy with subsequent normal growth. No newborn with clinical or biochemical thyroid dysfunctions was found. Two spontaneous abortions during the second month of pregnancy were recorded. One of two patients in question subsequently had two healthy children. On the basis of these data, previous administration of high 131I doses does not appear to be a valid reason for dissuading young female DTC patients from considering pregnancy. However, patients should be advised to avoid pregnancy after 131I administration for a period sufficient to ensure complete elimination of the radionuclide and to permit confirmation of complete disease remission, i.e. at least 1 year in our opinion.