Establishment of Trimester-Specific Reference Intervals for TSH and Thyroid Hormones in Pregnant Women living in Oran, Western Algeria.

Background and Aim: The thyroid gland undergoes physiological changes during pregnancy, leading to variations in reference intervals (RIs) for TSH and free thyroid hormones across the different trimesters. To ensure accurate interpretation of these tests, the American Thyroid Association (ATA) recommends the use of trimester-specific and population-based reference intervals. The aim of our study was: to establish trimester-specific reference intervals of TSH, FT3, and FT4 in pregnant women living in Oran western Algeria. Materials and Methods: The reference intervals were established accordingly to the CLSI guideline (EP28-A3c ). The study included 401 apparently healthy pregnant women, classified as follows: 120 in the first trimester, 154 in the second trimester, and 127 in the third trimester. Reference subjects were selected based on NACB exclusion criteria. Hormone assays were performed using the Roche Cobas e411 analyzer. Results: The established RIs corresponding to the 2.5th and 97.5th percentiles were in the First, Second and Third trimester for TSH: 0.25-3.57 mIU/L, 0.15-3.43 mIU/L,0.57-4.23 mIU/L, FT4 : 11.41-20 pmol/L, 10.56-18 pmol/L, 9.43-17.54 pmol/L, and FT3 : 3.16-7.02 pmol/L, 3.02-7.54 pmol/L, 3.2-7.37 pmol/L. Conclusion: In the absence of population-specific reference intervals for TSH and thyroid hormones in our country, establishing such values represents a significant advancement, enabling more accurate diagnosis and improved management of thyroid disorders.