Management of hypothyroidism during pregnancy

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:

• 1.Chakera AJ et al. Treatment for primary hypothyroidism: current approaches and future possibilities. Drug Des Devel Ther. 2012; 6: 1-11.
• 2.Abalovich M et al. Management of thyroid dysfunction during pregnancy and postpartum: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2007 Aug; 92(8 Suppl):S1-47.
• 3. Association for Clinical Biochemistry (ACB), British Thyroid Association (BTA), British Thyroid Foundation (BTF) 2006. UK guidelines for the use of thyroid function tests