Estimation of TSH reference intervals for the first trimester of pregnancy using real world data and the refineR...

Changes in the population and differences in pregnant women, as well as trimester-specific reference intervals (RIs), improve the interpretation of thyroid stimulation hormone (TSH). This study seeks to establish first trimester TSH RIs using the indirect method refineR algorithm.

A retrospective observational study was conducted at a Spanish laboratory's hospital during three years (February 2022 to March 2025). TSH results from 4717 outpatient women in their first trimester of gestation were extracted from the LIS. Most patients were of Caucasian ethnicity. After applying the exclusion criteria (positive thyroid antibodies; abnormal free thyroxine; reported free triiodothyronine; thyroid related diagnosis or follow-up thyroid tests), 4185 TSH results were included in the final dataset. Data management and statistical analyses were conducted using the refineR algorithm and Phyton. The RIs were verified with another dataset, which analysed 697 TSH results extracted during April and June 2025. Finally, the RIs were also verified with a direct prospective study including 24 pregnant women from a health care primary center. All analytes were measured using the electrochemiluminescence immunoassay analyser Cobas® 8000 (Roche, Basel, Switzerland).

The TSH RIs obtained for first trimester pregnant women, with 90 % CIs, were: 0.46 (CI 0.37-0.55) - 4.91 (CI 4.09-5.62) mIU/L.

This is the first study to establish RIs for TSH in the first trimester of pregnancy using the refineR methodology.