Abstract: Abstract Objective:　To evaluate the differences and reliability, we apply trimester-specific reference data created by Yan (Yan’s criteria) for diagnosis thyroid dysfunction of women during pregnancy, compared with population-based reference data (Adults’ criteria) . Methods: Totle samples we studied were 893 pregnant women during the three trimesters. The consistency of serum TSH and FT4 were detected. Both Yan’s and Adults’ criteria were applied to diagnosis thyroid dysfunction. Consistency rate and Kappa value were used to evaluate the validity and reliability of two types of criteria. Results: The medians of serum TSH concentration during pregnancy in the 1st, 2nd, 3rd trimesters were 1.72，2.27，2.38 mIU/L respectively; and the FT4 were 14.24, 13.36, 13.49 pmol/L. The prevalence of subclinical hypothyroidism diagnosed by Yan’s criteria during pregnancy is 10.5% compared with 7.5% by Adults’ criteria. The differences between them are mainly found in the 1st and 3rd trimesters. The revalence of hypothyroxinemia diagnosed by Yan’s criteria during pregnancy isse 2.6% compared with 11.0% by Adults’ criteria. The differences between them are found particularly in the 2nd and 3rd trimesters. Conclusion: Trimester-specific reference data of thyroid hormones established by Yan was confirmed to be more validity and reliability than population-based reference data during the three pregnant trimesters. The rates of missed diagnosis of subclinical hypothyroidism and misdiagnosis of hypothyroxinemia during pregnancy were decreased due to use of Yan’s criteria which was demonstrated more valuable in clinical practice.

Key words: pregnancy, thyroid, subclinical hypothyroidism, hypothyroxinemia, reference value