What is the recommended management for hyperthyroidism in pregnancy?

Management of Hyperthyroidism in Pregnancy

Hyperthyroidism in pregnant women should be treated with propylthiouracil (PTU) in the first trimester, followed by a switch to methimazole (MMI) for the second and third trimesters to minimize risks to both mother and fetus. 1

Diagnosis and Initial Evaluation

• TSH and Free T4 or Free T4 Index (FTI) testing should be performed in pregnant women with suspected hyperthyroidism 1
• Biochemical hyperthyroidism associated with hyperemesis gravidarum (undetectable TSH, elevated FTI) rarely requires treatment unless other signs of clinical hyperthyroidism are present 1
• Untreated hyperthyroidism during pregnancy increases risks of severe preeclampsia, preterm delivery, heart failure, miscarriage, and low birth weight 1

Medication Management

First Trimester

• Propylthiouracil (PTU) is the preferred medication during the first trimester 1, 2
• This recommendation is based on the association of methimazole with rare congenital anomalies including choanal atresia when used in early pregnancy 2, 3

Second and Third Trimesters

• Switch from PTU to methimazole after the first trimester 1, 2
• This switch is recommended due to the risk of severe hepatotoxicity associated with PTU 4, 2

Dosing and Monitoring

• The goal is to maintain Free T4 or FTI in the high-normal range using the lowest possible thioamide dosage 1
• Monitor Free T4 or FTI every 2-4 weeks to adjust medication dosage 1
• Beta blockers (e.g., propranolol) can be used temporarily to control symptoms until thioamide therapy reduces thyroid hormone levels 1
• TSH levels should be checked every trimester once stable 1

Special Considerations

Thyroid Storm in Pregnancy

• Thyroid storm is a medical emergency with high risk of maternal heart failure 1
• Treatment includes: propylthiouracil or methimazole, potassium/sodium iodide solutions, dexamethasone, and supportive care 1
• Diagnosis is based on fever, tachycardia disproportionate to fever, altered mental status, vomiting, diarrhea, and cardiac arrhythmia 1
• Delivery during thyroid storm should be avoided unless absolutely necessary 1

Fetal Monitoring

• Women with Graves' disease should be monitored for normal fetal heart rate and appropriate growth 1
• Routine ultrasound screening for fetal goiter is not necessary unless problems are detected 1
• The newborn's physician should be informed about maternal Graves' disease due to risk of neonatal thyroid dysfunction 1

Alternative Treatments

• Thyroidectomy should be reserved for women who do not respond to thioamide therapy 1
• Surgery is preferably performed during the second trimester if needed 1
• Radioactive iodine (I-131) is absolutely contraindicated during pregnancy 1
• Women should not breastfeed for four months after I-131 treatment 1

Postpartum Considerations

• Women treated with either propylthiouracil or methimazole can safely breastfeed 1
• Methimazole is the preferred medication during lactation 5
• Monitor for postpartum thyroiditis in women with history of thyroid dysfunction 1

Side Effects and Complications

• Monitor for agranulocytosis (presents with sore throat and fever), which requires immediate discontinuation of thioamide and complete blood count 1
• Other potential side effects include hepatitis, vasculitis, and thrombocytopenia 1
• Suppression of fetal and neonatal thyroid function with thioamide therapy is usually transient 1

Preconception Counseling

• Women with hyperthyroidism should ideally achieve euthyroidism before pregnancy 1
• Medication adjustments may be needed as thyroid dysfunction often diminishes as pregnancy progresses 1