Iodine 131 thyroid ablation in female children and adolescents: long-term risk of infertility and birth defects.
BACKGROUND: The use of radioactive iodine, or iodine 131 (131I), for remnant thyroid ablation and the treatment of cervical and distant metastatic disease in patients with thyroid cancer is well accepted. 131I concentrates in the bladder, and irradiation to the ovaries has been theorized to increase the risk of infertility and birth defects in subsequent offspring. METHODS: We conducted a retrospective review of the charts of 154 children and adolescents treated at our institution for thyroid cancer between 1951 and 1991. Review of these charts identified 68 females diagnosed with thyroid cancer, < or = 20 years of age, who received 131I as part of their therapy at our institution. Charts were reviewed and patients recontacted, and initial tumor, date of diagnosis, and 131I administration, including doses, were recorded. Complete pregnancy histories including current health status of the children were also recorded. RESULTS: Twenty-two patients who never attempted pregnancy were excluded from analysis. Eleven patients could not be contacted and were considered lost to follow-up and thus excluded from the study. In the remaining 35 patients, mean age at 131I administration was 18.3 years (range 14.1-20.8), mean follow-up, 16.8 years (range 5.6-39.8), and mean 131I dose, 148.53 mCi (range 77.2-250). Three patients were diagnosed infertile after extensive workup (8.6%). The remaining 32 patients had 69 pregnancies resulting in 60 term and four premature deliveries. There were two elective abortions for nonmedical reasons and three spontaneous abortions. Only two children were conceived within 1 year of 131I therapy. Both were born with birth defects that proved fatal within 8 months. No other children were born with birth defects. One other child born with an estimated gestational age of 27 weeks died due to complications related to his prematurity. No anomalies were noted at autopsy. Of the 61 children alive for follow-up, no major health problems were identified other than asthma in two children. CONCLUSIONS: 131I, used in doses up to 250 mCi, is not associated with any long-term risk of infertility. The risks of infertility or birth defects are not different from those of the general population. Because the two children with birth defects were born to mothers treated either during pregnancy or 6 months before conception, it might be wise to suggest avoiding pregnancy for up to 1 year after 131I treatment.