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KMID : 1101420180500010001
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Korean Journal of Clinical Laboratory Science
2018 Volume.50 No. 1 p.1 ~ p.10
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Evaluation of Pregnancy and Thyroid Function
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Park Chang-Eun
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Abstract
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During early pregnancy, before the development of a functioning thyroid gland, thyroid stimulating hormone (TSH) is a very sensitive marker of thyroid dysfunction during pregnancy. Normal values have been modified during gestation with a downward shift. The fetus is influenced by the TSH supplied by the mother. TSH and free thyroxine (FT4) concentrations vary during pregnancy and conventional units can vary between laboratories. A downward shift of the TSH reference range occurs during pregnancy, with a decrease in both the lower and upper limits of maternal TSH, relative to the typical non-pregnant TSH reference range. Each laboratory produces its own reference TSH and FT4 concentrations because there are many different assays that yield different results in pregnancy. Therefore, automated immunoassays used for serum FT4 analysis are still used widely, but the important considerations discussed above must be noted. The use of population-based, trimester-specific reference ranges remains the best way to handle this issue The slight downward shift in the upper reference range of TSH occurring in the latter first trimester (7~12 weeks) of pregnancy, typically not observed prior to 7 weeks. Their use indicates high or low levels in a quantitative manner independent of the reference ranges. These data highlight the importance of calculating population-based pregnancy-specific thyroid parameter reference intervals. A precision medicine initiative in this area will require the collection and analysis of a large number of genetic, biological, psychosocial, and environmental variables in large cohorts of individuals. Large prospective randomized controlled trials will be needed to resolve these controversies.
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KEYWORD
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Free T4, Pregnancy, Reference ranges, TSH
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