Answer to Question #8847 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I had a dose of 148 MBq of radioactive iodine to check for thyroid cancer recurrence. It was during ovulation. I am now six weeks pregnant. My obstetrician says there is going to be a problem because it was during ovulation. Will there be any birth defects? Will my baby be okay?
Your baby will not pick up any radioiodine in its thyroid until about 12 weeks gestation, so thyroid damage from the radioiodine is not possible. The mainly external radiation to your baby is about 7.1 millisievert, which is about two years worth of average natural background radiation in the United States, which is very low. It is not enough to cause any problem for your baby.
I can't promise that your baby will be perfect, because about 5 percent of babies are born with some kind of abnormality anyway, without extra radiation exposure. However, there will not be a problem from your low dose of radioactive iodine.
Carol S. Marcus, PhD, MD
Professor of Radiation Oncology and of Radiological Sciences, UCLA