The 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum clarify the parameters clinicians can use in shared decision making for the management of thyroid disease in pregnant women. The guidelines include areas of uncertainty, for example subclinical hypothyroidism, and examine whether women with subclinical hypothyroidism should be treated in pregnancy.
The American Thyroid Association recommends the following:
Maternal hypothyroidism is defined as a thyroid-stimulating hormone (TSH) concentration elevated beyond the upper limit of the pregnancy-specific reference range.
Pregnant women with TSH concentrations >2.5 milli-international units/L (mIU/L) should be evaluated for thyroid peroxidase antibody (TPOAb) status.
Levothyroxine therapy is recommended for:
Women who are TPOAb-positive with a TSH greater than the pregnancy-specific reference range.
Women who are TPOAb-negative who have a TSH greater than 10.0 mIU/L.
Patients usually present with nonspecific symptoms of weakness, lethargy, depression, and mild weight gain.
Commonly, disease is subclinical.
Physical exam may show dry skin, thick tongue, eyelid edema, and bradycardia.
Elevated TSH and low free T4.
Treatment is levothyroxine at a starting dose of 1.6 micrograms/kg daily or 25 micrograms daily in older patients or those with CAD.
Over-treatment is uncommon but can lead to iatrogenic hyperthyroidism.
Hypothyroidism is a clinical state resulting from underproduction of the thyroid hormones T4 and T3.  Most cases (95%) are due to primary hypothyroidism, a failure of the thyroid gland to produce thyroid hormones. The remaining 5% of cases are due to secondary hypothyroidism, underproduction of TSH by the pituitary gland.  Subclinical hypothyroidism is a state of usually asymptomatic, mild thyroid failure, with normal levels of T4 and T3, and minimal elevation of TSH.  Myxedema coma is a rare severe form of hypothyroidism with multiorgan failure. 
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Department of Family Medicine
University of North Carolina
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University of Chicago Medical Center
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Queen Elizabeth Hospital
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Caerphilly Miners' Hospital
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University of Copenhagen
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Texas Tech University Health Sciences Center - School of Medicine
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