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Management of hypothyroidism during pregnancy

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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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)

Reference:

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