TO THE EDITOR: We read with interest the article by Garsi et al. (1) concerning the pregnancy outcome and the health of offspring of women who had received 131I for differentiated thyroid cancer. In this article, the authors evaluated 2,673 pregnancies from patients treated with 131I and found 10.4% miscarriages before any treatment, 20% after thyroidectomy but before 131I therapy, and 19% after 131I therapy. There was no significant variation according to the cumulative 131I dose. The incidences of stillbirths, preterm births, low birth weight, and congenital malformations were not significantly different before and after 131I therapy. The authors concluded that there was no evidence that radioiodine therapy affected the outcomes of subsequent pregnancies and offspring.
Interestingly, we have reported a relatively similar study in a smaller number of patients. Our study predominantly examined the effect of 131I therapy (3,700 MBq) on menstrual cycle or pregnancy in women less than 40 y old. Specifically, we evaluated 45 women with differentiated thyroid cancer who were treated with 131I therapy and compared with 83 age-matched control women. We found menstrual cycle irregularities in 13.3% of patients before 131I therapy but 31.1% after treatment. However, after 131I therapy there were no subsequent pregnancy abnormalities such as premature births, miscarriages, or congenital abnormalities in the 7 children who were borne of 6 of the 45 patients (2). Another study, of 49 pregnancies from 76 patients who received 131I therapy, found 10% miscarriages, 18% induced abortions, and no congenital malformations or first-year mortality (3). All these findings concur that 131I therapy is safe regarding subsequent pregnancy outcome. However, our results suggest an increased incidence of menstrual cycle abnormalities after 131I therapy. It will be interesting to see if Garsi et al. (1), in their large cohort of patients, noticed any such abnormalities induced by 131I therapy.
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