Hyperthyroidism tends to occur in young and middle-aged women, and a number of patients have a desire to have children. In terms of fertility needs, the choice of iodine 131 treatment is preferred and is most appropriate for treatment to a mildly hypothyroid state. Why is this so? First of all, hyperthyroidism is not suitable for pregnancy. On the one hand, it is difficult to conceive in hyperthyroidism, and on the other hand, even if conception is successful, it is easy to miscarry. Of course, there are cases in which a healthy child is born after a successful pregnancy in a hyperthyroid state. However, this is a rare case and the risk is very high, so we do not recommend it. For hyperthyroidism treated with iodine 131, there can be some cases after treatment as follows: 1. After treatment, thyroid function returns to normal (it is better to check FT3, FT4 and TSH in normal range for 2-3 months continuously, which is a stable improvement), if the patient has been treated with iodine 131 for more than six months at this time, then the patient can prepare for pregnancy. However, during pregnancy preparation, iodine must be avoided and rest and strain must be observed, otherwise a few patients may experience a relapse of hyperthyroidism. This is because pregnancy is also a period when hyperthyroidism is likely to recur, especially for patients with a family history of hyperthyroidism. 2. If hypothyroidism occurs after iodine 131 treatment, you should give Eugenol replacement therapy and gradually increase the dose until FT3, FT4 and TSH are all in the normal range and stable for 2-3 months. At this point, you can start to prepare for pregnancy, but during the preparation period, you need to check FT3, FT4 and TSH every month and adjust the dose of Eugenol in time according to the test results. In my clinical practice, dozens of hypothyroid patients have successfully conceived and given birth to healthy babies after replacement therapy. 3.If hyperthyroidism is not cured after 1 course of iodine 131 treatment (half year), you can proceed to the second course of iodine 131 treatment until it is cured or hypothyroidism. Then, refer to the situation described above, you can eventually have a baby successfully. As for the ideal treatment to mild hypothyroidism, it is because patients with mild hypothyroidism usually do not have recurrence of hyperthyroidism, and because the degree of hypothyroidism is light, so you can not take Eugenol in hot weather, and a small amount of Eugenol in cold weather is enough.