There are two types of gestational reference values, one is the gestational reference value established by our hospital or region, and the other is the reference value recommended by guidelines. For example, the 2011 ATA guidelines first proposed TSH reference values specific to the three stages of pregnancy, i.e., 0.1-2.5 mIU/L in T1; 0.2-3.0 mIU/L in T2; and 0.3-3.0 mIU/L in T3. Factors affecting TSH measurement values in the normal population include the iodine nutritional status and measurement reagents in the region. This guideline lists the reference ranges of serum TSH in four groups of pregnant women established by the First Hospital of China Medical University (Shenyang), General Hospital of Tianjin Medical University and International Peace Maternity and Child Health Hospital of Shanghai Jiao Tong University School of Medicine. 5.17 mIU/L (Roche reagent), and 4.51 mIU/L (Bayer reagent). (See Table 2.) Given that the upper reference values established by each region and hospital vary greatly, they are significantly higher than the upper limit of 2.5 mIU/L recommended by the ATA guidelines. Therefore, this guideline recommends that each region and hospital establish their own TSH reference values for pregnant women. The diagnostic criteria for clinical hypothyroidism in pregnancy are: TSH > upper limit of the reference value in pregnancy and FT4 < lower limit of the reference value in pregnancy. 2011 version of ATA guideline also suggests that women with t1 pregnancy with tsh > 10 mIU/L can be diagnosed as clinical hypothyroidism regardless of FT4 reduction. However, there is no academic consensus on the criterion of TSH>10mIU/L. The diagnostic criteria for clinical hypothyroidism in pregnancy are: serum TSH > the upper limit of the reference value in pregnancy (97.5 th) and serum FT4 < the lower limit of the reference value in pregnancy (2.5 th).