Establishment of trimester-specific reference intervals for thyroid hormones in Korean pregnant women.
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.
Department of Laboratory Medicine, Konkuk University School of Medicine, Seoul, Korea.
Hee-Won
HW
Moon
Department of Laboratory Medicine, Cheil General Hospital and Women's Healthcare Center, Kwandong University College of Medicine, Seoul, Korea.
Hee-Jung
HJ
Chung
Department of Laboratory Medicine, Dongnam Institute of Radiological and Medical Sciences, Busan, Korea.
Chul-Min
CM
Park
Department of Laboratory Medicine, Konkuk University School of Medicine, Seoul, Korea.
Mina
M
Hur
Department of Laboratory Medicine, Konkuk University School of Medicine, Seoul, Korea.
Yeo-Min
YM
Yun
D000328:Adult; D044466:Asian People; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000592:standards; D008163:Luminescent Measurements; D011247:Pregnancy; D011264:Pregnancy Trimesters; D011295:Prenatal Care; D012016:Reference Values; D056910:Republic of Korea; D013963:Thyroid Hormones / Q000032:analysis* / Q000592:standards; D013974:Thyroxine / Q000032:analysis* / Q000592:standards
D013963:Thyroid Hormones; D013974:Thyroxine
FT4; Korean; Pregnancy; Reference interval; TSH; Trimester