First of all, it is important to know why “iodine potion” (iodine 131) can treat “”thyroid cancer”. “Hyperthyroidism” is the abbreviation for hyperthyroidism. “Thyroid cancer” refers to the most common type of thyroid cancer – differentiated thyroid cancer (including papillary thyroid cancer and follicular thyroid cancer). The normal human thyroid gland has the function of secreting (“producing”) thyroid hormones, which regulate the metabolism of various substances in the human body, maintain the excitability of the human nervous system and other needs of growth and development of infants and children. The production of thyroid hormones is essential, and the main raw material is iodine, which is absorbed by the thyroid gland in most cases. In differentiated thyroid cancer, there are functional cancer cells with certain thyroid cells in the cancer cells including metastases. These cancer cells, can absorb iodine just like normal cells. Iodine 131 is a radioactive substance that is involved in the synthesis of thyroid hormones, just like the iodine in our food. In this way, when thyroid cells or differentiated thyroid cancer cells absorb iodine 131, the radioactivity produced by iodine 131 can kill the thyroid cells, thyroid cancer cells, and thus achieve the purpose of treatment. When iodine 131 is used to treat thyroid cancer, the residual thyroid tissue is small and the thyroid cancer cells themselves are relatively weak in absorbing iodine. As a result, a large amount of iodine 131 is not absorbed and finally excreted through the gastrointestinal tract and urinary tract. Therefore, during iodine 131 treatment, patients are usually required to stay in a special hospital ward, and their feces and urine are handled centrally to avoid causing adverse effects to others. In this way, after iodine 131 treatment, most of the iodine 131 in the body is excreted and the patient can come into contact with others as in daily life. However, since the reproductive organs are exposed to some radiation during iodine 131 treatment and the thyroid function is low before iodine treatment, all of these can affect the success of fertility and treatment, so it is generally recommended to prepare for pregnancy after six months of iodine 131 treatment. During pregnancy, there is no difference from the general pregnancy except that the dosage of thyroid hormone is increased appropriately.