Reference Values During Pregnancy

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Thyroid Stimulating Hormone (TSH)

   Units Nonpregnant Adult First Trimester Second Trimester Third Trimester

µIU/mL or mIU/L

0.34 - 4.25 0.6 - 3.4 0.37 - 3.6 0.38 - 4.04


0.34 - 4.25 0.6 - 3.4 0.37 - 3.6 0.38 - 4.04


  0.1 - 2.5 * 0.2 - 3* 0.3 - 3*

*References ranges recommended by the American Thyroid Association if trimester-specific reference ranges for TSH are not available in the laboratory.

Some causes of elevated TSH include primary hypothyroidism (Hashimotos thryroiditis), TSH secreting pituitary tumor, thyroid hormone resistance, insufficient T
4 therapy for hypothyroidism, adrenal insufficiency, iodine, lithium, and antithyroid drugs.

When maternal TSH is elevated, measurement of serum FT4 concentration is necessary to classify the patient's status as either subclinical (SCH) or overt hypothyroidism (OH). SCH is defined as a serum TSH between 2.5 and 10 mIU/L with a normal FT4 concentration. Women with a TSH concentration above the trimester-specific reference interval with a decreased FT4, and all women with a TSH concentration above 10.0 mIU/L irrespective of the level of FT4  are also considered to have OH. [3]

Some causes of low TSH levels include, hyperthyroidism (Graves' disease),  stimulation of the TSH receptor by hCG (first trimester of pregnancy, hyperemesis gravidarum, molar pregnancy/choriocarcinoma), exogenous thyroid hormone, thyroiditis, an autonomous thyroid nodule, dopamine, glucocorticoids, secondary hypothyroidism.


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. 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

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