*References ranges recommended by the American Thyroid Association
if trimester-specific reference ranges for TSH are not available in the
laboratory.
ELEVATED TSH:
Some causes of elevated TSH include primary
hypothyroidism (Hashimotos thryroiditis), TSH secreting pituitary tumor, thyroid
hormone resistance, insufficient T4
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]
LOW TSH :
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.
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. 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
