What is the recommended treatment for hypothyroidism (underactive thyroid) in pregnant women?

Management of Hypothyroidism in Pregnancy

Levothyroxine is the treatment of choice for hypothyroidism in pregnant women, with dosage adjusted to maintain TSH within the normal reference range. 1

Initial Treatment Approach

• For women diagnosed with hypothyroidism during pregnancy:

  • Start levothyroxine immediately to normalize TSH levels 1, 2
  • Prompt treatment is essential to prevent adverse maternal and fetal outcomes including:
    • Increased risk of preeclampsia
    • Preterm delivery
    • Heart failure
    • Miscarriage
    • Low birth weight
    • Potential neurocognitive defects in offspring 1, 2

• For women already on levothyroxine before pregnancy:

  • Increase the dose by approximately 30% as soon as pregnancy is confirmed 3
  • This proactive approach helps maintain euthyroidism during early pregnancy when fetal brain development is critical

Dosing and Monitoring Protocol

Dosage Adjustments

• Increase levothyroxine dosage every 4 weeks until TSH is stable 1
• The magnitude of required increase varies by trimester and etiology of hypothyroidism:
  • First trimester: 30-50% increase from baseline 3, 4
  • Second trimester: 26-55% increase from baseline 5, 4
  • Third trimester: 26-62% increase from baseline 5, 4

Monitoring Schedule

• Check TSH levels every 4-6 weeks during pregnancy 1, 2
• Monitor more frequently after initial dose adjustments
• Target TSH within normal reference range 1, 2

Special Considerations by Etiology

• Primary hypothyroidism: Requires smaller increases (11-16%) 5
• Post-treatment Graves' disease: Requires largest increases (27-51%) 5
• Post-thyroidectomy for cancer: Moderate increases (9-26%) 5

Postpartum Management

• Return to pre-pregnancy levothyroxine dose immediately after delivery 2
• Monitor TSH 6-8 weeks postpartum to confirm appropriate dosing 2

Potential Pitfalls and Caveats

• Failure to increase dose early: Most dose adjustments are needed by the 8th week of gestation 3
• Inadequate monitoring: TSH should be checked every trimester even in stable patients 1
• Overlooking drug interactions: Certain foods (soybean flour, walnuts, dietary fiber) and medications can affect levothyroxine absorption 2
• Assuming all patients need dose increases: While 84% of women require increased dosing, approximately 7-9% may need decreased doses or no change 4
• Mistaking pregnancy-related symptoms for thyroid dysfunction: Careful clinical assessment is needed

Subclinical Hypothyroidism in Pregnancy

• Women with subclinical hypothyroidism who are pregnant or planning pregnancy should receive levothyroxine therapy 1
• This recommendation is based on potential associations between elevated TSH and:
  • Increased fetal loss
  • Possible neuropsychological complications in offspring 1

By following this structured approach to managing hypothyroidism in pregnancy, clinicians can help ensure optimal maternal and fetal outcomes while minimizing the risks associated with untreated or undertreated hypothyroidism.