Therapeutic administration of 131I for differentiated thyroid cancer: radiation dose to ovaries and outcome of pregnancies.

UNLABELLED Radiation is known to be mutagenic. The present study updates a 10-y-old study regarding pregnancy outcome and the health of offspring of women previously exposed to radioiodine ((131)I) during thyroid carcinoma treatment, by doubling the number of pregnancies that occurred after exposure. METHODS Data on 2,673 pregnancies were obtained by interviewing female patients who were treated for thyroid carcinoma but had not received significant external radiation to the ovaries. RESULTS The incidence of miscarriages was 10% before any treatment for thyroid cancer; this percentage increased after surgery for thyroid cancer, both before (20%) and after (19%) (131)I treatment, with no variation according to the cumulative dose. In contrast to previously reported data, miscarriages were not significantly more frequent in women treated with radioiodine during the year before conception, not even in women who had received more than 370 MBq during that year. The incidences of stillbirths, preterm births, low birth weight, congenital malformations, and death during the first year of life were not significantly different before and after (131)I therapy. The incidences of thyroid and nonthyroid cancers were similar in children born either before or after the mother's exposure to radioiodine. CONCLUSION There is no evidence that exposure to radioiodine affects the outcomes of subsequent pregnancies and offspring. The question as to whether the incidences of malformations and thyroid and nonthyroid cancers are related to gonadal irradiation remains to be established. The doubling dose is still being heatedly debated, and the value of 1 Gy as the doubling dose in humans should be reevaluated.