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Management of hypothyroidism during pregnancy

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Requires specialist advice.

Maintenance of the euthyroid state is the aim of management during pregnancy:

  • in women with hypothyroidism diagnosed before pregnancy and who are already taking thyroxine
    • for hypothyroid women planning pregnancy, levothyroxine dose ideally should be adjusted to keep TSH less than 2.5 mIU/L before conception (1,2)
    • thyroid function should be checked as soon as the pregnancy is confirmed to adjust the dose of levothyroxine further
    • at the first prenatal visit the dose is usually increased by 30-50% (as early as four to eight weeks' of gestation)
      • some studies have suggested an increase by 30% as soon as the woman finds out that she is pregnant (before evaluation) to minimize early maternal hypothyroidism
      • an alternative approach is to advise the woman to increase the dose of levothyroxine by 30%-50% as soon as pregnancy is confirmed to avoid any delay in dose increment (1)
    • the increase in dose varies with the cause of hypothyroidism e.g. - in women without any residual thyroid tissue, the dose should be increased more rapidly to a greater amount and than those with Hashimoto's thyroiditis (3)
    • thyroid function should be monitored at regular intervals (every 4-6 weeks) to adjust the dose of levothyroxine to keep TSH under 2.5 mIU/L in the first trimester and under 3.0 mIU/L in the second and third trimesters (2)
      • patients will need a reduction of their levothyroxine dose after pregnancy (1)

  • in women with overt hypothyroidism diagnosed during pregnancy
    • aim is to normalise the thyroid function test as soon as possible (3)
    • thyroxine dose should be adjusted to reach and maintain serum TSH concentrations in the low normal range (0.4 - 2.0mU/L) in the first trimester (or trimester specific normal TSH values) (2)
    • thyroid function test should be repeated during therapy - four to five weeks after the onset and every six weeks thereafter (3)
  • in women with thyroid autoimmunity who are euthyroid during early stages of pregnancy
    • elevation of TSH above the normal values should be monitored (3)

  • in women with subclinical hypothyroidism
    • thyroxin therapy is associated with improved obstetrical outcome but does not modify long-term neurological development of the fetus
    • the American Endocrine Society recommends thyroxine replacement in pregnant women with subclinical hypothyroidism (3)
    • there is general consensus that subclinical hypothyroidism in pregnant women should also be treated with levothyroxine (1,2)


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