What is the recommended management for a pregnant patient with known Graves' disease (Hyperthyroidism)?

Management of Graves' Disease in Pregnancy: A Comprehensive MFM Consult

The recommended management for a pregnant patient with known Graves' disease includes propylthiouracil (PTU) during the first trimester followed by methimazole for the second and third trimesters, with the goal of maintaining free T4 or FTI in the high-normal range using the lowest possible thioamide dosage. 1

Diagnosis and Assessment

• Confirm hyperthyroidism with suppressed TSH and elevated T3 and T4 levels, which in pregnancy is most commonly due to Graves' disease 2
• Differentiate from gestational transient thyrotoxicosis (hyperemesis gravidarum), which can present with biochemical hyperthyroidism but rarely requires treatment 2
• Monitor maternal and fetal well-being as untreated maternal hyperthyroidism increases risks of severe preeclampsia, preterm delivery, heart failure, miscarriage, and low birth weight 3, 1

Treatment Algorithm

Medication Management

• First Trimester:

  • Use propylthiouracil (PTU) as the preferred antithyroid medication 1, 2
  • This recommendation is based on concerns about potential methimazole-associated congenital anomalies 4

• Second and Third Trimesters:

  • Switch to methimazole after the first trimester 1, 2
  • This switch reduces the risk of PTU-associated hepatotoxicity 5

• Dosing Strategy:

  • Use the lowest effective dose to maintain FT4 or FTI in the high-normal range 3, 1
  • Aim for mild maternal hyperthyroidism to prevent fetal hypothyroidism 6
  • Monitor FT4 or FTI every 2-4 weeks to guide dosage adjustments 3, 1
  • Check TSH level once each trimester 2

• Symptom Management:

  • A beta-blocker (e.g., propranolol) can be used temporarily to control symptoms until thioamide therapy reduces thyroid hormone levels 3, 2

Monitoring for Medication Side Effects

• For PTU:

  • Monitor for hepatotoxicity - liver function tests should be performed periodically 7
  • Watch for signs of agranulocytosis (fever, sore throat) which typically occurs within first 3 months of treatment 7, 8
  • Be alert for vasculitis which can involve small blood vessels of skin, kidneys, or lungs 7

• For Methimazole:

  • Monitor for vasculitis - symptoms may include new rash, hematuria, decreased urine output, dyspnea or hemoptysis 5
  • Check prothrombin time before surgical procedures due to potential hypoprothrombinemia 5

Fetal Assessment and Management

• Monitor fetal heart rate and growth throughout pregnancy 3, 2
• Ultrasound screening for fetal goiter is not necessary unless problems are detected 3
• Inform the newborn's physician about maternal Graves' disease due to risk of neonatal thyroid dysfunction 3, 1

Special Considerations

Thyroid Storm Management

• Thyroid storm is a medical emergency requiring immediate treatment 3
• Presentation includes fever, tachycardia out of proportion to fever, altered mental status, vomiting, diarrhea, and cardiac arrhythmia 3
• Treatment includes PTU or methimazole, potassium/sodium iodide solutions, dexamethasone, and supportive care 2

Alternative Treatments

• Thyroidectomy should be reserved only for women who do not respond to thioamide therapy 3, 8
• Radioactive iodine (I-131) is absolutely contraindicated during pregnancy 3

Postpartum Considerations

• Women treated with PTU or methimazole can safely breastfeed 3, 5
• Consider definitive treatment (radioiodine or surgery) after pregnancy to prevent recurrence in future pregnancies 9

Common Pitfalls to Avoid

• Failure to monitor thyroid function regularly during pregnancy may result in inadequate treatment 1
• Not switching from PTU to methimazole after the first trimester increases the risk of hepatotoxicity 1
• Maintaining maternal free T4 in the normal range may still result in fetal hypothyroidism - aim for high-normal or slightly elevated maternal thyroid function 9, 6
• Limiting PTU prescriptions to the amount required until the next scheduled visit helps ensure proper monitoring, especially for patients who might continue medication without supervision 9