CLINICAL THYROIDOLOGY FOR PATIENTS
A publication of the American Thyroid Association

Summaries for Patients from Clinical Thyroidology by Ernest Mazzaferri, MD MACP
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NONTHYROIDAL EFFECTS OF RADIOIODINE

Abbreviations & Definitions

Radioiodine (131I) is used to treat papillary follicular and Hürthle cell cancer (differentiated thyroid cancer).appo 30 to 100 mCi of 131I is used for thyroid remnant ablation to destroy residual thyroid tissue and to facilitate follow-up of patients with thyroglobulin and whole body radioiodine scans. Patients with metastases are treated with approximately 100 to 200 mCi.

What is the study about? The effect of radioiodine on the ovaries and offspring over a 10 year period

The full article title: “Therapeutic Administration of 131I for Differentiated thyroid cancer: radiation dose to ovaries and outcome of pregnancies” It is in the May 2008 issue of the Journal of Nuclear Medicine (Volume 18, Issue 59, pages 854-52. The authors are JP Garsi, M Schlumberger,C Rubino, M Ricard, M Labbe,C Ceccarelli, C Schvartz, M Henri-Amar, S Bardet, and F De Vathaire, F. The abstract can be obtained from:

http://www.ncbi.nlm.nih.gov/pubmed/18413399?dopt=Citation

What is known about the problem being studied? Ten years ago this group reported that radioiodine (131I) therapy for thyroid cancer had no effects on the outcome of subsequent pregnancies and offspring in women treated for thyroid cancer, with the exception of miscarriages in a small number of women that occurred during the first year after 131I therapy.

What was the aim of the study? The study was designed to assess the rate of induced abortions, miscarriage, stillbirth, prematurity, birth weight below the 10th percentile for gestational age, congenital abnormalities, and death during the child’s first year of life and the development of thyroid disease in children, including tumors at other sites.

Who was studied? Study subjects were 1126 women with differentiated thyroid cancer who had a total of 2078 pregnancies. In this group, 44% were given 100 mCi or more of 131I in 1 to 11 treatments that were administered a mean of 35 months (range, 0 to 243) before conception.

How was the study done? From 1994 to 2004 all the women treated for thyroid cancer at the Institut Gustave-Roussy in Paris and the Institut Jean Godinoit in France and at the Institute of Endocrinology in Pisa were routinely interviewed by trained data managers, who collected information regarding the following features of each pregnancy.

What were the results of the study? A total of 341 therapeutic and elective abortions were done, 65% before treatment, and 8% after thyroid cancer surgery alone, and 28% after both surgery and 131I therapy. Induced abortions were more frequent after surgical therapy, both with and without 131I therapy, than before any treatment had been done. Higher cumulative amounts of 131I (10 to 100 mCi) before pregnancy were not associated with a greater probability of an induced abortion. A total of 18 induced abortions of 34 pregnancies occurred in women who had received ≥10 mCi 131I during the year before conception, which was a greater proportion of abortions than occurred in pregnancies preceded by smaller amounts of 131I.

Miscarriages were observed in 193 of 1857 pregnancies (10%) before any thyroid cancer treatment was administered, and were more frequent (21%) in pregnancies that occurred after surgery alone, but were about the same before (20%) and after (19%) 131I therapy. There was no correlation between the cumulative amount of 131I therapy of and the occurrence of miscarriage.

Among the 2009 live births, none of the following appeared to be modified by mother’s previous surgery or 131I exposure: prematurity, low birth weight, death before 1 year, malformation, thyroid disease, and cancers. In all, 1.3% of 1633 died less than 37 weeks after birth, 22 were before mothers were given treatment and 3 after the mother’s surgery for thyroid cancer

How does this compare with other studies? This is the largest study of patients with the longest follow-up of the published literature.

What are the Limitations of this study? The main limitation of the study is that fetal malformations and loss were not compared to the general population in France and Italy because the two countries coded these two outcomes differently.

What are the implications of this study? Radioiodine therapy for women with thyroid cancer does not adversely affect subsequent pregnancies and offspring over a 10-year follow-up period. There was no correlation between the cumulative amount of 131I therapy of and the occurrence of miscarriage.

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