Abstract： Objective To investigate the state of thyroid hormones and thyrotropin level in different gestation periods. Methods FT3, FT4, TSH and hCG were measured in 623 patients by ACS-180 automatic chemiluninescence analyzer. The urinary iodine was random measured by the use of iodine catalytic reaction mechanism of Arsenic-Cerium, rapid urinary iodine was detected with cold digestion method of quantitative detection. Result Serum FT3,FT4 ,and hCG levels in the first and second trimester were higher than in the third trimester ( F =53. 19,78.00,58.77, P ＜0. 05) ,and TSH levels were lower than in the third trimester ( F =5.68, P ＜0.05). The incidence of thyrotropin level disorder was 7. 54%, there were no significant differences in the gestation periods ( χ2 = 3.92, P ＞ 0. 05 ). The incidence of subclinical hypothyroidism,subclinical hyperthyroidism, hypothyroidism and hyperthyroidism were 3.53%, 2. 57%, 1.12% and 0. 32%, respectively. The incidence of subclinical hypothyroidism in the first and third trimester was high, while the incidence of subclinical hyperthyroidism in the second trimester was high. Conclusions Thyrotropin level in the third trimester was lower than that of the first and second trimester. HCG changes were not the main reason that caused the thyrotropin level disorder during the pregnancy.