Reference Intervals for Thyroid Hormones During the First Trimester of Gestation: A Report from an Area with a Sufficient Iodine Level
- 1Isfahan Endocrine and Metabolism Research Center, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
- 2Department of Biostatistics & Epidemiology, School of Public Health, Isfahan University of Medical Sciences, Isfahan, Iran.
- 3Department of Radiology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
- 4Department of Engineering and Mathematics, Sheffield Hallam University, Sheffield, UK.
- 5Mayo Clinic College of Medicine, Rochester, Minnesota, USA.
- #Contributed equally.
The physiological changes during pregnancy modulate the endocrine system. Therefore, both the American and the European thyroid associations recommend the use of local trimester-specific reference intervals. The purpose of this study was to establish the first trimester reference intervals for thyroid function tests in the central area of Iran. We examined 436 pregnant women in their first trimester of pregnancy, and 444 non-pregnant women in a cross sectional study. Serum levels of thyroid stimulating hormone (TSH), free thyroxin (FT4), free triiodothyronine (FT3), thyroid peroxidase antibody, urinary iodine concentration (UIC), and thyroid volume were measured for all subjects. The first trimester-specific reference intervals (2.5th-97.5th percentile) were determined for 185 pregnant women and 256 non-pregnant women with negative TPOAb, adequate iodine level (UIC≥150 μg/l in pregnant and UIC≥100 μg/l in non-pregnant women), and normal thyroid examination. We calculated multiples of the median (MoM) for TFTs to normalize the obtained data. The first trimester-specific reference intervals of serum TSH, FT4, and FT3 for pregnant women were 0.20-4.60 mIU/l, 9.0-18.02 pmol/l, and 3.40-5.64 pmol/l, respectively, while the corresponding figures for non-pregnant women were 0.59-5.60 mIU/l, 9.52-19.30 pmol/l, and 3.70-5.55 pmol/l, respectively. The first and 99th percentile MoM of TSH in pregnant women in their first-trimester was 0.06-4.62. The local normal reference ranges for the first trimester of pregnancy in central region of Iran were different from the ranges suggested by the ATA.
Keywords: pregnancy, first trimester, gestation, thyroid function test, TPOAb, TSH, reference interval, multiples of the median (MoM)
How to Cite
Kianpour M, Aminorroaya A, Amini M, Feizi A, Janghorbani M, Shokri S, Yamini SA, Farghadani M, Hekmatnia A, Gharib H. Reference Intervals for Thyroid Hormones During the First Trimester of Gestation: A Report from an Area with a Sufficient Iodine Level. Horm Metab Res. 2019 Mar;51(3):165-171. doi: 10.1055/a-0855-7128. Epub 2019 Mar 12. Erratum in: Horm Metab Res. 2021 Sep;53(9):638-640. PMID: 30861562.