A 31 year old female with a recent history of miscarriage presented with abnormal thyroid function tests and was history of low dose levothyroxine use. She complained of a 3 month history of extreme fatigue, palpitations and 18 pound weight loss at the time of presentation. Her thyroid stimulating immunoglobulin was 9.21 IU/L (0-0.55), free thyroxine 6.2ng/dL (0.9-1.8), free triiodothyronine 20.04 pg/mL (1.8-4.6) with a suppressed TSH 0.01 uIU/ml (0.27 - 4.2). She was started on methimazole. Her 24 hour radioactive iodine uptake was 60% and she subsequently underwent radioactive iodine-131 ablation in capsule form. She failed the ablation after 7 months and remained on methimazole during that duration. Her second radioactive iodine uptake was 58% and she underwent a second RAI ablation. Her TSH was 50 uIU/ml and her free thyroxine was 0.1 ng/dl. She was started on levothyroxine for replacement. Patient unexpectedly became pregnant approximately six weeks after her radioactive iodine treatment.
Studies have shown that with the exception of miscarriages, there is no evidence that exposure to radioiodine affects the outcome of subsequent pregnancies and offspring. Although the number of children born of mothers exposed to radioiodine is relatively small, the present data indicates that there is no reason for patients exposed to radioiodine to avoid pregnancy. The only adverse effect observed in the study series is an increased incidence of miscarriages in women exposed to therapeutic radioiodine during the year which preceded conception. The fetus would be at risk due to maternal hypothyroidism.
Conclusion: Pregnancies achieved after exposure to radioactive iodine treatment do not appear to be at increased risk for negative outcomes. Nevertheless, it is recommended that pregnancy be avoided for 1 year following radioactive iodine therapy to allow reproductive function to normalize.