Hypothyroidism and
Pregnancy — the Importance
of TSH Management7

The 2017 American Thyroid Association guidelines provide recommendations for the management of hypothyroidism and TSH during pregnancy

Management of thyroid diseases during pregnancy requires special considerations because pregnancy can induce major changes in thyroid function.

Serum TSH values should be obtained as soon as pregnancy is confirmed in the following women at high risk for thyroid disease:

  • A history of hypothyroidism/hyperthyroidism or current symptoms/signs of thyroid dysfunction
  • Known thyroid antibody positivity
  • Presence of goiter
  • History of head or neck radiation or prior thyroid surgery
  • Age > 30 years
  • History of Type 1 diabetes or other autoimmune disorders
  • History of pregnancy loss, preterm delivery, or infertility
  • Multiple prior pregnancies (≥2)
  • Family history of autoimmune thyroid disease or thyroid dysfunction
  • Morbid obesity (BMI ≥ 40 kg/m2)
  • Use of amiodarone or lithium, or recent administration of iodinated radiologic contrast
  • Residing in an area of known moderate to severe iodine insufficiency

Recommendation BEFORE Pregnancy

Treated hypothyroid patients (receiving LT4) who are planning pregnancy should have serum TSH evaluated preconception and their LT4 dose adjusted to achieve a TSH value between the lower reference limit and 2.5 mU/L.

Recommendation DURING Pregnancy

In pregnant patients with treated hypothyroidism, maternal serum TSH should be monitored approximately every 4 weeks during the first half of pregnancy and at least once near 30 weeks gestation, because further LT4 dose adjustments may be required.

For patients with serum TSH above the normal trimester-specific range, increase the dose of Synthroid by 12.5 to 25 mcg/day and measure TSH every 4 weeks until a stable Synthroid dose is reached and serum TSH is within the normal trimester-specific range.

Recommendation AFTER Pregnancy

The necessary LT4 dose adjustments during gestation are a function of pregnancy itself. Therefore, following delivery, LT4 should be reduced to the patient’s preconception dose. Additional TSH testing should be performed at approximately 6 weeks postpartum.

Thyroid Function Test

Thyroid function test results of healthy pregnant women differ from those of healthy nonpregnant women, as well as by population.

Population and trimester-specific reference ranges for serum TSH during pregnancy should be used, determined by each provider's institute/laboratory.

If not feasible, apply pregnancy-specific TSH reference ranges for similar patient populations under similar conditions.

If neither internal nor transferable pregnancy-specific TSH reference ranges are available, an upper reference limit of ~4.0 mU/L may be used.

When treating hypothyroidism in pregnant women, consider a target TSH in the lower half of the trimester-specific reference range. If unavailable, strive for TSH values below 2.5 mU/L.

Indication and Important Safety Information for Synthroid


SYNTHROID® (levothyroxine sodium) tablets, for oral use is indicated as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism.

Pituitary Thyrotropin (Thyroid Stimulating Hormone, TSH) Suppression
SYNTHROID is indicated as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.

Limitation of Use1

SYNTHROID is not indicated for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients, as there are no clinical benefits and over-treatment with SYNTHROID may induce hyperthyroidism.

SYNTHROID is not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis.

Important Safety Information1


Thyroid hormones, including SYNTHROID, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects.

  • SYNTHROID is contraindicated in patients with uncorrected adrenal insufficiency.
  • In the elderly and in patients with cardiovascular disease, SYNTHROID should be initiated at lower doses than those recommended in younger individuals or in patients without cardiac disease. If cardiac symptoms develop or worsen, the SYNTHROID dose should be reduced or withheld for one week and restarted at a lower dose.
  • Patients with coronary artery disease who are receiving SYNTHROID should be monitored closely during surgical procedures for cardiac arrhythmias. Monitor patients during concomitant administration of SYNTHROID and sympathomimetic agents for signs and symptoms of coronary insufficiency.
  • Use of oral thyroid hormone is not recommended in myxedema coma. Products formulated for IV administration should be used to treat myxedema coma.
  • Patients with adrenal insufficiency should be treated with replacement glucocorticoids prior to initiating treatment with SYNTHROID. Failure to do so may precipitate an acute adrenal crisis when thyroid hormone therapy is initiated.
  • SYNTHROID has a narrow therapeutic index. Regardless of the indication for use, careful dosage titration is necessary to avoid the consequences of over- or under-treatment.
  • Addition of levothyroxine therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements. Carefully monitor glycemic control after starting, changing, or discontinuing SYNTHROID.
  • Increased bone resorption and decreased bone mineral density may occur as a result of levothyroxine over-replacement, particularly in postmenopausal women. To mitigate this risk, patients receiving SYNTHROID should be given the minimum dose necessary that achieves the desired response.  
  • Adverse reactions associated with SYNTHROID therapy are primarily those of hyperthyroidism due to therapeutic overdosage.
  • Many drugs and some foods affect thyroid hormone pharmacokinetics and metabolism and may alter the therapeutic response to SYNTHROID. In addition, thyroid hormones and thyroid status have varied effects on the pharmacokinetics and actions of other drugs. Administer at least 4 hours before or after drugs that are known to interfere with absorption. Evaluate the need for dose adjustments when regularly administering within one hour of certain foods that may affect absorption. Prescribers should consult appropriate reference sources for additional information on drug or food interactions with SYNTHROID.
  • SYNTHROID should not be discontinued during pregnancy, and hypothyroidism diagnosed during pregnancy should be promptly treated. TSH levels may increase during pregnancy, so TSH should be monitored and SYNTHROID dose adjusted as needed.