Reference intervals of thyroid hormones during pregnancy in Korea, an iodine-replete area.
Maternal thyroid dysfunction has been associated with adverse pregnancy outcomes. The purpose of our study was to establish trimester-specific reference intervals for thyroid hormones in pregnant women in Korea, where iodine intake is more than adequate and to examine pregnancy and perinatal outcomes in their offspring.



Among 459 healthy pregnant women who were screened, we enrolled 417 subjects who had negative results for thyroid autoantibodies. Serum thyroid stimulating hormone (TSH) and free thyroxine were measured using an immunoradiometric assay. Urine iodine concentration was measured using inductively coupled plasma-mass spectrometry in 275 women. Reference ranges of thyroid hormones were determined according to the guidelines of the National Academy of Clinical Biochemistry. Pregnancy and perinatal outcomes were compared according to maternal thyroid function.



The reference ranges of serum TSH were 0.03 to 4.24 mIU/L in the first trimester, 0.13 to 4.84 mIU/L in the second trimester, and 0.30 to 5.57 mIU/L in the third trimester. Pregnancy and perinatal outcomes did not vary in mothers with subtle changes in thyroid function.



Trimester-specific thyroid hormone reference intervals in Korean pregnant women differ from those of other countries with different iodine nutrition status and ethnicity. The establishment of population-based, reliable trimester-specific reference intervals is critical for the interpretation of thyroid function in pregnant women to avoid unnecessary tests and treatments.
Division of Endocrinology and Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.|Division of Endocrinology and Metabolism, Department of Internal Medicine, Soonchunhyang University Hospital Seoul, Seoul Korea.
Hye Jeong
HJ
Kim
Division of Endocrinology and Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.|Division of Endocrinology and Metabolism, Department of Medicine, Gyeongsang National University School of Medicine, Jinju, Korea.|Department of Medicine, Institute of Health Sciences, Gyeongsang National University School of Medicine, Jinju, Korea.
Yoon Young
YY
Cho
Division of Endocrinology and Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Sun Wook
SW
Kim
Division of Endocrinology and Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Tae Hyuk
TH
Kim
Department of Medical Education, Sungkyunkwan University School of Medicine, Seoul, Korea.
Hye Won
HW
Jang
Department of Laboratory Medicine and Genetics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Soo-Youn
SY
Lee
Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Suk-Joo
SJ
Choi
Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Cheong-Rae
CR
Roh
Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Jong-Hwa
JH
Kim
Division of Endocrinology and Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Jae Hoon
JH
Chung
Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Soo-Young
SY
Oh
D000328:Adult; D005260:Female; D006801:Humans; D007455:Iodine; D007564:Japan; D011247:Pregnancy / Q000502:physiology; D011248:Pregnancy Complications / Q000175:diagnosis; D012016:Reference Values; D056910:Republic of Korea; D013959:Thyroid Diseases / Q000175:diagnosis; D013960:Thyroid Function Tests; D013963:Thyroid Hormones / Q000097:blood; D013972:Thyrotropin; D013974:Thyroxine
D013963:Thyroid Hormones; D013972:Thyrotropin; D007455:Iodine; D013974:Thyroxine
Iodine; Pregnancy; Reference intervals; Republic of Korea; Thyroid hormones