What is the management for a 34-year-old female (YOF) at 13 weeks gestation with hyperemesis gravidarum and severe hyperthyroidism, indicated by a Thyroid-Stimulating Hormone (TSH) level of less than 0.01 milli-international units per liter (mIU/L)?

Management of Hyperthyroidism in Hyperemesis Gravidarum

For a 34-year-old female at 13 weeks gestation with hyperemesis gravidarum and TSH <0.01mIU/L, no specific treatment for the hyperthyroidism is usually required as this likely represents transient biochemical hyperthyroidism associated with hyperemesis gravidarum rather than true clinical hyperthyroidism requiring intervention.

Understanding the Condition

• Hyperemesis gravidarum is commonly associated with biochemical hyperthyroidism, characterized by undetectable TSH levels and elevated free T4 index (FTI), but this is rarely associated with clinical hyperthyroidism requiring treatment 1
• This transient hyperthyroidism typically resolves spontaneously as pregnancy progresses and hyperemesis improves 2, 3
• The hyperthyroidism is likely mediated by high levels of human chorionic gonadotropin (hCG), which has weak thyroid-stimulating activity 2

Diagnostic Approach

• Further evaluation should include:
  • Free T4 and Free T3 levels to assess the degree of hyperthyroidism 1
  • Assessment for clinical signs of hyperthyroidism (tachycardia, tremor, heat intolerance) 2
  • Absence of thyroid autoantibodies would support transient gestational thyrotoxicosis rather than Graves' disease 2

Management Algorithm

1. For Transient Hyperthyroidism with Hyperemesis Gravidarum:

• Focus treatment on the hyperemesis rather than the hyperthyroidism 1:

  • Intravenous hydration and correction of electrolyte abnormalities 1
  • Antiemetic therapy as recommended by ACOG 1
  • Nutritional support and thiamine supplementation to prevent Wernicke's encephalopathy 1

• Monitor thyroid function:

  • Repeat thyroid function tests every 2-4 weeks until normalized 1
  • Most cases resolve by 18-20 weeks gestation 3, 4

2. If Clinical Hyperthyroidism is Present:

• If the patient has persistent symptoms of hyperthyroidism despite treatment of hyperemesis, consider:
  • Short-term beta-blocker (propranolol) for symptom control until thyroid hormone levels normalize 1
  • Antithyroid medication only if clear clinical hyperthyroidism persists 1, 5

3. If Graves' Disease is Suspected:

• If clinical features suggest Graves' disease (goiter, ophthalmopathy) or thyroid autoantibodies are positive:
  • Propylthiouracil is preferred in the first trimester 6
  • Consider switching to methimazole in the second and third trimesters due to potential hepatotoxicity with propylthiouracil 6, 7
  • Goal is to maintain FT4 or FTI in the high-normal range using the lowest possible thioamide dosage 1
  • Monitor FT4 or FTI every 2-4 weeks 1

Important Considerations

• Differentiation between transient hyperthyroidism and Graves' disease is crucial as management differs significantly 8
• The severity of hyperemesis often correlates with the degree of hyperthyroidism 4
• Patients with transient hyperthyroidism may have abnormal electrolytes and liver enzymes 4
• Unnecessary antithyroid treatment should be avoided in transient hyperthyroidism 2

Monitoring and Follow-up

• Monitor for resolution of hyperemesis and improvement in thyroid function 3
• If hyperthyroidism persists beyond 20 weeks, reconsider the diagnosis and potential need for treatment 3
• Monitor fetal growth and heart rate if maternal hyperthyroidism is significant 1

Potential Complications

• Untreated significant maternal hyperthyroidism can increase risk of:

  • Maternal heart failure
  • Spontaneous abortion
  • Preterm birth
  • Fetal or neonatal hyperthyroidism 6, 7

• Antithyroid medications carry risks:

  • Propylthiouracil: hepatotoxicity (particularly concerning in pregnancy) 6
  • Methimazole: potential teratogenic effects in first trimester 7
  • Both: agranulocytosis, vasculitis 6, 7