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Classification of Thyroid Dysfunction in Pregnant Women Differs by Analytical Method and Type of Thyroid Function
Stine Linding Andersen1,2,3, Peter Astrup Christensen1,3, Louise Knøsgaard1,3
1Department of Clinical Biochemistry, Aalborg University Hospital, Aalborg, Denmark.
The Journal of Clinical Endocrinology and Metabolism
|August 25, 2020
Summary
Maternal thyroid function testing shows significant variation based on pregnancy week, analytical method, and test type. Establishing specific reference ranges is crucial for accurate diagnosis of thyroid dysfunction during pregnancy.
Area of Science:
- Endocrinology
- Clinical Chemistry
- Reproductive Medicine
Background:
- Maternal thyroid function assessment is complicated by physiological changes during pregnancy.
- Establishing accurate reference ranges for thyroid function tests (TFTs) by gestational week is essential but remains challenging.
- Variability in TFT classification based on analytical methods and test types necessitates further investigation.
Purpose of the Study:
- To establish pregnancy week- and method-specific reference ranges for key thyroid function tests.
- To compare the classification of maternal thyroid dysfunction using different analytical methods and TFTs.
- To assess the impact of reference range variations on diagnosing thyroid disorders in pregnant women.
Main Methods:
- Serum samples from 6282 Danish pregnant women were analyzed for thyrotropin (TSH), total and free thyroxine (T4), total and free triiodothyronine (T3), and T-uptake.
- Two analytical methods (Method A and Method B) were used for TSH and free T4 measurements.
- Reference ranges were derived from 4612 thyroid antibody-negative women, considering pregnancy week and analytical method.
Main Results:
- Thyrotropin (TSH) levels decreased, while total T4, total T3, and T-uptake increased gradually from weeks 4-14 of pregnancy.
- Free T4 and free T3 showed minimal variation across pregnancy weeks.
- Classification of abnormal thyroid function differed significantly between Method A and Method B, and between total T4 and free T4 assays.
Conclusions:
- Maternal thyroid dysfunction classification is highly dependent on the analytical method and type of thyroid function test used.
- Even with established week- and method-specific reference ranges, considerable variability in diagnostic outcomes persists.
- Standardization of thyroid function testing methodologies and reference ranges in pregnancy is critical for accurate clinical management.
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