Reference Intervals of Thyroid Function Tests in First Trimester Vietnamese Pregnant Women.

Background: Although TSH suppression by elevated β-hCG is essentially seen during first trimester, differences in TSH reference ranges between various countries have been reported. Physiologic changes during pregnancy may also influence FT4 assays. This study aims to establish method-specific reference intervals (RIs) of TSH, FT4, and FT3 in Vietnamese, first trimester pregnant women.