Iodine is an essential trace element for the human body and is one of the raw materials necessary for the synthesis of thyroid hormones. It is one of the essential nutrients to ensure normal growth and development of the fetus, especially the normal development of the brain and nerves. The development of the fetus requires the mother to provide thyroid hormone on the one hand, and the fetal thyroid gland to synthesize thyroid hormone by itself on the other. Therefore, only when both the mother’s and the fetal thyroid glands are working properly can the fetus be supplied with sufficient amounts of thyroid hormones to meet the normal needs of the fetus. In order for the fetal thyroid gland to work properly, in addition to the normal development, differentiation and maturation of the fetal thyroid gland, it is also necessary for the mother to provide sufficient amounts of iodine, the raw material necessary for the synthesis of thyroid hormones. Adequate iodine intake by the mother enters the fetus through the placenta for the fetal thyroid gland to synthesize thyroid hormones. Therefore, the amount of iodine that a mother needs to take during pregnancy is much more than the amount of iodine she takes during normal, non-pregnant periods. The iodine supplementation during pregnancy supplies the mother’s own thyroid gland for the synthesis of thyroid hormones on the one hand, and the fetus in the womb for the synthesis of thyroid hormones by the fetal thyroid gland on the other. How much iodine should a mother take during pregnancy? The World Health Organization recommends a daily intake of 250ug of dietary iodine for pregnant mothers during pregnancy and 150ug for non-pregnant women. So, how can pregnant women supplement iodine to meet the daily intake of 250ug of dietary iodine? With regard to the natural iodine status in China, except for areas with naturally high iodine levels, the amount of iodine provided by the natural environment and dietary intake in most areas is far below this requirement. Therefore, additional iodine supplementation is needed. In China, especially for the general public, the most convenient, effective and relatively stable daily intake method is iodine supplementation through salt. Since the amount of salt consumed per day is relatively fixed for each person, and the amount of iodine added to salt is also fixed, the corresponding amount of iodine supplementation can be calculated from the amount of salt consumed. Some people have a low daily salt intake and a low daily iodine intake through salt supplementation, in that case, additional iodine supplementation is needed. Some people buy salt from overseas or abroad through the internet, so they need to know whether iodine is added to it and the amount of iodine added to it (some countries do not add iodine to salt), and if it is not added or the amount is not enough, they also need additional iodine supplementation. In some cases, if you change your place of living during pregnancy, you will need to adjust the use of iodized salt according to your place of living, as the amount of salt iodized varies from region to region. In short, pregnancy requires more iodine intake than usual, non-pregnant periods to meet the needs of the mother and fetus. In today’s age of diversity, each pregnant mother needs to adjust her daily iodine intake according to her own situation. As long as the proper daily intake of iodine is ensured, the fetus can grow and develop normally and have a healthy and smart baby.