Related Experiment Video
Updated: Feb 1, 2026

Author Spotlight: Advancing Labor Management Through Electromyometrial Imaging for Understanding Uterine Contractions
Published on: May 26, 2023
Reference TSH levels in Spanish pregnant women. Is it possible to unify criteria?
Sergio Donnay Candil1, Amelia Oleaga Alday2, Elías Álvarez-García3
1Unidad de Endocrinología y Nutrición, Hospital Universitario Fundación Alcorcón, Alcorcón (Madrid), España.
Introduction:
Specific TSH and free thyroxine ranges are needed to adequately assess maternal thyroid function during pregnancy.
Aim:
The aim of this review is to review studies reporting data on references TSH and free thyroxine levels in Spanish women during the first trimester of pregnancy.
Material And Methods:
Literature search and selection of studies providing reference TSH ranges in the first trimester of pregnancy.
Results:
The TSH cut-off point to define hypothyroidism (P97.5) was different depending on the immunoassay used. Gestational age, thyroid autoimmunity, and maternal iodide nutritional status can determine the variability seen in the results.
Conclusions:
Differences found in the studies do not allow for establishing a unified TSH reference range. However, results suggest that the TSH upper reference limit is close to 4μU/mL. Reference TSH ranges specific for each population and immunoassay during pregnancy should be defined.
Related Concept Videos
Criteria for Causality: Bradford Hill Criteria - II
Criteria for Causality: Bradford Hill Criteria - I
Inertial Frames of Reference
Non-inertial Frames of Reference
Chemical Shift: Internal References and Solvent Effects
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
Leveling Effect

