[Objective]To establish the reference intervals of thyroid hormones in pregnant women from Sanming city and compare them with those from other areas in China.[Methods]The study recruited 605 pregnant women and 229 non-pregnant healthy women who visited Sanming First Hospital between March 29 and June 28,2023.Blood samples were se-quentially collected from the participants to determine the serum levels of thyroid stimulating hormone(TSH),free triiodo-thyronine(FT3)and free thyroxine(FT4).The reference intervals of thyroid hormones were established by using a percen-tile range of P2.5 to P97.5 and their changes in different periods of pregnancy were analyzed and compared with those from oth-er areas in China.[Results]There were significant differences in levels of TSH,FT4 and FT3 at different periods of pregnan-cy(all P<0.05).Compared with non-pregnant women,women in first trimester had significantly decreased levels of TSH and FT4,but similar level of FT3.Since the second trimester,TSH level displayed rising tendency,while FT3 and FT4 lev-els showed gradual decrease.The reference intervals of thyroid hormones in the first,second and third trimester of pregnan-cy in Sanming city were TSH(0.068,2.943)μU/mL,FT3(4.302,6.888)pmol/L,FT4(8.240,14.719)pmol/L;TSH(0.419,3.274)μU/mL,FT3(4.074,6.629)pmol/L,FT4(6.726,11.980)pmol/L;TSH(0.422,3.570)μU/mL,FT3(3.741,5.850)pmol/L,FT4(6.103,10.347)pmol/L,respectively.Significant differences were found in the reference in-tervals of thyroid hormones during pregnancy among different areas in China.[Conclusions]The levels of TSH,FT3,FT4 during pregnancy are different from those during non-pregnancy,and also significantly differ in different periods of preg-nancy.Reference intervals of thyroid hormones in pregnant women are affected by various factors such as geographic loca-tion,ethnicity and laboratory test method,etc.Therefore,establishing the population-specific reference intervals of thy-roid hormones will benefit for the diagnosis and treatment of thyroid disease in pregnant women from Sanming city.