Korean J Perinatol.  2009 Dec;20(4):332-338.

TSH and Free T4 Concentrations in Korean Pregnant Women

• Jo YS
• Kim DM
• Lee GS
• Kim MJ
• Kim SJ

Abstract

PURPOSE
To determine the means, medians and reference intervals for TSH (thyroid-stimulating hormone) and fT4 (free thyroxine) for each month of gestation and for three trimesters in Korean pregnant women.
METHODS
Serum samples were collected from 265 pregnant women with singleton gestation. Levels of TSH, fT4 were measured by immunoassay. After exclusion of subjects with positive antimicrosomal autoantibodies, the means, medians and reference intervals based on 2.5th and 97.5th percentiles for TSH, fT4 were determined.
RESULTS
The study population consisted of 94 women in first trimester, 49 women in second trimester, and 122 women in third trimester. The trimester-specific reference intervals were: TSH (1st trimester: 0.03~2.72, 2nd: 0.27~2.29, and 3rd: 0.03~2.88 mIU/L), fT4 (1st trimester 4.50~19.75, 2nd: 4.70~12.98 and 3rd: 5.07~11.84 pg/mL). fT4 levels were significantly lower in the second and third trimesters. TSH levels were lower in the first trimester than second and third trimester, with gradual elevation in the second and third trimester.
CONCLUSION
Levels of TSH, fT4 during pregnancy differ from those in non-pregnant women. Gestational age specific reference intervals will play a cental role in screening and diagnosis of thyroid disorders. Further studies for normal reference ranges during pregnancy are needed to create reference intervals in Korean pregnant women.

Keyword

Thyroid function test; TSH; FT4; thyroid-stimulating hormone; free thyroxine; reference intervals

MeSH Terms

Autoantibodies
Female
Gestational Age
Humans
Immunoassay
Mass Screening
Pregnancy
Pregnancy Trimester, First
Pregnancy Trimester, Second
Pregnancy Trimester, Third
Pregnant Women
Reference Values
Thyroid Function Tests
Thyroid Gland
Thyrotropin
Autoantibodies
Thyrotropin