Thyroid abnormalities are not uncommon in patients with recurrent miscarriages. The survey showed that the rate of early miscarriage, preterm birth and fetal malformation in patients with abnormal thyroid function (hypo-, hypo- or hyperthyroidism) and positive simple thyroid antibodies is higher than that in normal patients. However, miscarriage, preterm delivery and fetal malformation do not always occur in patients with abnormal thyroid function or positive simple thyroid antibodies, and the reasons for this have not yet been understood. I have encountered a large number of patients with recurrent miscarriages who have asked me some questions in the clinic. Today, I would like to bring more comprehensive and scientific answers to my patients. For the most focused questions, let me give you a few more tips: 1. Many of you have asked whether you must adjust your TSH to below 2.5 before pregnancy. According to the American Thyroid Association’s 2011 guidelines, it is necessary to do so. My advice: a Further check FT4, TPO-AB, and TG-AB, TSH can be rechecked more than one month apart, and if there are problems with the above, supplementation with LT4 should be considered. b Yes, if there are no problems with the above tests, and TSH alone is slightly above 2.5, supplementation is always beneficial and it is always good to be cautious. C. If you have a history of adverse pregnancy, are over 30 years old, have a family history of abnormal thyroid function, or have a history of thyroid surgery, you should supplement with LT4. 2. What is the normal range of thyroid function during pregnancy? According to ATA 2011 guidelines, the following reference values are recommended: 0.1-2.5 mIU/L in the first trimester, 0.2-3.0 MIU/L in the second trimester, and 0.3-3.0 MIU/L in the third trimester. 3. How to diagnose hypothyroidism and subclinical hypothyroidism in pregnancy? TSH over 2.5 mIU/L in pregnancy with FT4 reduction. TSH over 10.0mIU/L is considered clinical hypothyroidism, regardless of whether FT4 is normal or not. Subclinical hypothyroidism: TSH during pregnancy is between 2.5 and 10.0 mIU/L, with normal FT4 concentration. 4. Guidelines on the diagnosis and management of hypothyroidism in pregnancy (Shen Ying et al., 2011). a If the pregnant woman’s TSH is higher than 10 mIU/L, treatment is required regardless of the FT4 concentration. Isolated hypotrichosis in stage b does not require treatment (some experts recommend treatment). c Although subclinical hypothyroidism may have adverse effects on the pregnant woman and fetus, the need for treatment of subclinical hypothyroid pregnant women with negative thyroid antibodies with levothyroxine T4 (LT4) is not well documented due to the lack of randomized controlled studies (given the adverse effects of subclinical hypothyroidism, on balance, many experts recommend LT4 treatment for subclinical hypothyroidism, and the American Endocrine Society also recommends LT4 treatment). LT4 treatment). d Pregnant women with subclinical hypothyroidism should be treated with LT4 if they are positive for TPOAb (there is no consensus among experts, but some experts recommend clinical treatment with LT4 for the same reasons as above). e. LT4 is recommended for the treatment of hypothyroidism in pregnancy, and other thyroid agents such as T3 or thyroxine tablets are not recommended. f. The goal of FT4 therapy is to normalize maternal serum TSH values (0.1 to 2.5 mIU/L at 1 to 3 months; 0.2 to 3.0 mIU/L at 4 to 6 months; 0.3 to 3.0 mIU/L at 7 to 9 months). g. If a pregnant woman with subclinical hypothyroidism is not treated, serum TSH and FT4 should be tested every 4 weeks until 16 to 20 weeks of gestation to alert for progression to clinical hypothyroidism. This strategy has not been confirmed in prospective studies. g. In patients with hypothyroidism treated with LT4, if menopause or a positive home pregnancy test occurs, further clarification of pregnancy is needed and the LT4 dose should be increased by 25% to 30% in women with confirmed pregnancy. A simpler approach is to change from one dose of LT4 per day before pregnancy to nine doses of LT4 per week, which increases the LT4 dose by approximately 29%. The need for an increase in LT4 dose during pregnancy varies widely, with some women requiring only a 10% to 20% increase and others requiring an 80% increase, so individualized therapy is needed, but it is important to maintain TSH within the normal range during pregnancy. i For women with hypothyroidism who are planning to become pregnant, adjust the dose of LT4 prior to pregnancy to keep the TSH below 2.5 mIU/L before becoming pregnant, as lower levels of TSH prior to pregnancy (within the normal reference range for non-pregnant women) may reduce the likelihood of increased TSH in the first trimester. k For pregnant women on LT4 therapy, TSH should be monitored every 4 weeks during the first half of pregnancy, as the LT4 dose is often adjusted based on TSH values. (18) In postpartum hypothyroidism, the LT4 dose should be restored to the pre-pregnancy dose and TSH should be measured 6 weeks after delivery. k In treated Hashimoto’s thyroiditis patients, no other tests such as other maternal thyroid tests, fetal ultrasound, etc. are recommended except for maternal thyroid function. The test should be performed on the fetus, fetal ultrasound, cord blood sample, etc., unless there are abnormalities in the pregnancy. For pregnant women with positive thyroid antibodies but normal thyroid function who are not receiving LT4 therapy, the possibility of hypothyroidism should be monitored during pregnancy, and TSH should be monitored every 4 weeks during the first half of pregnancy and at least once during the 26th and 32nd weeks of pregnancy. m Although randomized controlled studies have confirmed that treatment with selenium during pregnancy reduces the incidence of postpartum thyroiditis, there are no follow-up studies to confirm or refute this finding. m Although randomized controlled studies have confirmed that selenium treatment during pregnancy reduces the incidence of postpartum thyroiditis, there are no follow-up studies to confirm or refute this finding, so selenium is not currently recommended for use in TPO-positive pregnant women.