Original Article

Ann Lab Med 2015; 35(2): 198-204

Published online March 1, 2015

Copyright © Korean Society for Laboratory Medicine.

Establishment of Trimester-Specific Reference Intervals for Thyroid Hormones in Korean Pregnant Women

Hee-Won Moon, M.D.1,*, Hee-Jung Chung, M.D.2,*, Chul-Min Park, M.D.3, Mina Hur, M.D.1, and Yeo-Min Yun, M.D.1

Department of Laboratory Medicine1, Konkuk University School of Medicine, Seoul; Department of Laboratory Medicine2, Cheil General Hospital and Women’s Healthcare Center, Kwandong University College of Medicine, Seoul; Department of Laboratory Medicine3, Dongnam Institute of Radiological and Medical Sciences, Busan, Korea

Correspondence to: Yeo-Min Yun
Department of Laboratory Medicine, Konkuk University School of Medicine, 120-1 Neungdong-ro, Gwangjin-gu, Seoul 143-729, Korea
Tel: +82-2-2030-5582
Fax: +82-2-2030-5587
*These two authors equally contributed to this manuscript.

Received: August 7, 2014; Revised: September 12, 2014; Accepted: December 29, 2014

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


Background: Establishment of trimester- and assay-specific reference intervals for every population is recommended. The aim of this study was to establish a trimester- and assay-specific reference interval for thyroid-stimulating hormone (TSH) and free thyroxine (FT4) in Korean pregnant women.
Methods: From April 2012 to December 2012, 531 pregnant women receiving prenatal care and 238 age-matched, non-pregnant women were enrolled in this study. After excluding patients with pregnancy-associated complications or thyroid-specific autoantibody, 465 pregnant and 206 non-pregnant women were included. Non-parametric analysis (2.5-97.5th percentile) was performed to determine the reference interval. Levels of TSH and FT4 were determined by electrochemiluminescence immunoassay (Elecsys thyroid tests, Roche Diagnostics, Germany).
Results: The TSH reference intervals were 0.01-4.10, 0.01-4.26, and 0.15-4.57 mIU/L for the first, second, and third trimester, respectively. From the first trimester to the third trimester, the median TSH levels showed a significantly increasing trend (P<0.0001). The FT4 reference intervals were 0.83-1.65, 0.71-1.22, and 0.65-1.13 ng/dL for the first, second, and third trimester, respectively, showing a significantly decreasing trend (P<0.0001).
Conclusions: Establishing trimester-specific reference intervals in pregnant women is essential for accurate assessment of thyroid function. Our population-specific and method-specific reference intervals will be useful for screening Korean pregnant women for thyroid disease.

Keywords: TSH, FT4, Reference interval, Korean, Pregnancy, Trimester