From my research, the guidelines about when it's safe to father a child after radioactive iodine treatment vary widely. His doctor said a year, but I've also seen pages that say 6 months or as little as two months (I'll send you the link). I would not only tell your OBGYN, but also contact his doctor and maybe even get a second opinion by another doctor experienced with radioactive iodine.
I know that exposure to radioactive iodine during pregnancy can damage the baby's thyroid gland, but I can't seem to find any information about what the risks are to getting pregnant after treatment. Perhaps enough of it stays in the body that there could be exposure, even months later. Only a doctor can tell for sure.
Don't panic until you talk to the doctors and see what they think. Good luck. Please write back and tell us what you found out.