Answer to Question #11871 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
My husband and I were intimate the day before I went in to have radioactive iodine treatment to kill off my thyroid. I did not know this, but he removed his protection while we were together. Is there any way I could still get pregnant from this time or did the dosage kill off any potential sperm that would be left? I do not know the medical lingo but I know the dosage they gave me started with the number 20.
It is difficult to say whether the sperm would be killed or not. Based on your suggestion that the dose was 20 something (I believe it would be 20 millicuries [mCi] or 740 megabecquerels [MBq] of iodine-131 [131I]), the dose to the ovaries would not be enough to cause issues, but sperm tend to be a bit more sensitive to radiation than eggs in the ovaries. So I cannot say with firm conviction whether or not the sperm would have survived.
On a different note, if you did become pregnant, the good news is (besides being pregnant) that there would be no harm caused by the radiation from the iodine treatment. There is a period early in pregnancy where, if you become pregnant after radiation exposure, there is no harm to the baby.
I'm sorry I can't give you a firm yes or no answer to your question, but if you are pregnant, congratulations and know that the radiation will not cause any harm.
Certified Medical Health Physicist
U.S. Nuclear Regulatory Commission. Radiation dose estimates for radiopharmaceuticals. Washington, DC: Nuclear Regulatory Commission; NUREG/CR-6345; 1996.