Reference Values For Thyroxine, free in Pregnancy

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Reference Values During Pregnancy

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Thyroxine free, Thyroxine direct, FT₄ , Free T₄,Unbound T₄(serum)

Units	Nonpregnant Adult	First Trimester	Second Trimester	Third Trimester
ng/dL	0.8 - 1.7	0.8- 1.2	0.6 - 1	0.5 - 0.8
pmol/L	10.3 - 21.9	10.3 - 15.5	7.7 - 12.9	6.4 - 10.3

Isolated hypothyroxinemia is defined as a normal maternal TSH concentration in conjunction with FT4 concentrations in the lower 5th or 10th percentile of the reference range.

References:

1. Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009 Dec;114(6):1326-31. PMID:19935037
2. Brent GA.Maternal thyroid function: interpretation of thyroid function tests in pregnancy. Clin Obstet Gynecol. 1997 Mar;40(1):3-15.
PMID: 9103946
3. Fischbach FT, Dunning MB III, eds. A Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia, Lippincott Williams and Wilkins,2004
4. 3. Stagnaro-Green A, ert al. American Thyroid Association Taskforce on Thyroid Disease During Pregnancy and Postpartum.Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and postpartum. Thyroid. 2011 Oct;21(10):1081-125.PMID .21787128