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Updated: Jul 5, 2026
An Ex vivo Culture System to Study Thyroid Development
Published on: June 6, 2014
Free thyroxine reference interval in each trimester of pregnancy determined with the Roche Modular E-170
Yanping Gong1, Barry R Hoffman
1Department of Laboratory Medicine and Pathobiology, University of Toronto, Canada.
Objective:
To determine using a simplified study design trimester-specific FT4 reference intervals in pregnancy with the Roche Modular immunoassay in routine use.
Design And Methods:
Surplus blood from 300 women in each trimester, drawn at documented times in the gestation, and from 40 age-matched nonpregnant women were assayed for FT4, thyroid stimulating hormone (TSH) and antithyroid peroxidase autoantibody (anti-TPO).
Results:
After excluding women positive for anti-TPO and with abnormal TSH, reference intervals were calculated as 12.5-19.1 pmol/L (nonpregnant group), 11-19 pmol/L (first trimester), 9.7-17.5 pmol/L (second trimester) and 8.1-15.3 pmol/L (third trimester). 3rd trimester FT4 was significantly lower than that of the second trimester (p<0.001) which, in turn, was lower than that of the first trimester (p<0.001). FT4 reference intervals in pregnancy were significantly lower than in the nonpregnant women (p<0.002).
Conclusions:
The observed trimester-specific FT4 reference intervals progressively decline with advancing gestation and differ significantly from one another.
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