Thyroid-stimulating Hormone (TSH) in Pregnancy

CPT: 84443
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Test Details


  • Thyrotropin in Pregnancy


Assessment of thyroid function during pregnancy


Electrochemiluminescence Immunoassay (ECLIA)

Reference Interval


• First trimester: 0.100−4.000

• Second trimester: 0.200−4.000

• Third trimester: 0.300−4.000

• Nonpregnant adult: 0.450−4.500

Additional Information

Thyroid function test results of healthy pregnant women differ from those of healthy nonpregnant women. During pregnancy there are significant changes in the thyroid gland. The size of the gland increases slightly, production of thyroid hormones increase by about 1.5 times, and subsequently iodine demand increases. T4-binding globulin (TBG) concentrations increase in response to estrogens. Thyrotrophic activity of hCG results in a decrease in serum TSH in the first trimester. During pregnancy, therefore, women may have somewhat lower serum TSH concentrations than before pregnancy. In twin pregnancies the downward shift of TSH can be greater than in singleton pregnancies.

Serum TSH and its reference range gradually rise in the second and third trimesters, but it is noteworthy that the TSH reference interval remains lower than in nonpregnant women. However, the 2017 ATA guidelines have recommended shifting the upper limit from 2.5 to 4.0 based on recent large studies. In a small percentage of women, TSH can be very suppressed (<0.01 mIU/mL) and yet still represent a normal pregnancy. There are slight but significant ethnic differences in serum TSH concentrations. African American and Asian women have TSH values that are on average 0.4 mIU/mL lower than in Caucasian women; these differences persist during pregnancy.1 This assay has a sensitivity of 0.004 uIU/mL and meets all criteria as a third-generation TSH assay.

Specimen Requirements




0.8 mL

Minimum Volume

0.3 mL (Note: This volume does not allow for repeat testing.)


Red-top tube or gel-barrier tube


If red-top tube is used, transfer separated serum to a plastic transport tube.

Storage Instructions

Room temperature. Stable at room temperature, refrigerated, or frozen for 14 days. Freeze/thaw cycles: stable x3

Causes for Rejection

Citrate plasma specimen; improper labeling

Clinical Information

Special Instructions

This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.


  • 1. Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid. 2017 Mar;27(3):315-389.28056690


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
004593 TSH Pregnancy 11580-8 004591 TSH Pregnancy uIU/mL 11580-8

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