Establishment of trimester-specific reference range for thyroid hormones during pregnancy

Area of Science:

• Endocrinology
• Reproductive Health
• Clinical Biochemistry

Background:

• Thyroid function undergoes significant physiological changes during pregnancy.
• Accurate interpretation of thyroid markers necessitates pregnancy-specific reference ranges.
• Existing ranges may not accurately reflect thyroid function in pregnant populations.

Purpose of the Study:

• To determine trimester-specific reference ranges for key thyroid markers in healthy pregnant Iranian women.
• To establish reliable intervals for thyrotropin (TSH), thyroxine (T4), free thyroxine index (FT4I), and thyroid peroxidase antibody (TPOAb).

Main Methods:

• A self-sequential study analyzed data from 314 pregnant Iranian women.
• Serum levels of TSH, T4, FT4I, and TPOAb were measured across the 1st, 2nd, and 3rd trimesters.
• Trimester-specific reference intervals were calculated using the 2.5th and 97.5th percentiles via statistical modeling.

Main Results:

• Estimated reference intervals for TSH, T4, and FT4I were provided for each trimester.
• The first-trimester reference interval for TPOAb was established.
• TSH levels showed a trend of increasing from the first to the second trimester, then slightly decreasing, with variations observed across gestational age percentiles.

Conclusions:

• The study successfully generated trimester-specific reference ranges for common thyroid markers in healthy pregnant Iranian women.
• These ranges are vital for preventing biochemical misinterpretations in thyroid testing during pregnancy.
• The findings support the need for localized, pregnancy-adjusted reference values in clinical practice.