What is the appropriate treatment for a pregnant patient with hyperthyroidism?

From the Guidelines

The appropriate treatment for a pregnant patient with hyperthyroidism primarily involves antithyroid medications, with propylthiouracil (PTU) preferred during the first trimester and methimazole (MMI) typically used for the remainder of pregnancy. This approach is based on the most recent and highest quality evidence available, which prioritizes minimizing fetal exposure while effectively managing the mother's condition 1.

Key Considerations

• PTU is recommended at 50-300 mg daily in divided doses during early pregnancy because it has less risk of causing the rare birth defect of aplasia cutis compared to methimazole.
• After the first trimester, switching to methimazole (5-30 mg daily) is often advised as it has better efficacy and requires less frequent dosing.
• The goal is to maintain maternal free T4 levels at or slightly above the upper limit of normal using the lowest effective dose of medication.
• Beta-blockers like propranolol (10-40 mg every 6-8 hours) can be used temporarily for symptom control, particularly for palpitations and tremors.
• Close monitoring is essential with thyroid function tests every 2-4 weeks initially, then every 4-6 weeks once stabilized.
• Medication doses should be reduced as pregnancy progresses since hyperthyroidism often improves naturally.

Important Safety Information

• Surgery (thyroidectomy) is rarely performed during pregnancy but may be considered in the second trimester if medication fails or causes severe side effects.
• Radioactive iodine treatment is absolutely contraindicated during pregnancy as it can destroy the fetal thyroid gland.
• The treatment of hyperthyroidism in pregnancy is crucial to prevent severe preeclampsia, preterm delivery, heart failure, and possibly miscarriage, as well as low birth weight in neonates 1.
• Fetal thyrotoxicosis needs to be considered in women who have a history of Graves' disease, and appropriate consultation should be sought if this condition is diagnosed.

From the FDA Drug Label

Particular care should be exercised with patients who are receiving additional drugs known to cause agranulocytosis. Pregnancy Category D See WARNINGS If methimazole is used during the first trimester of pregnancy or if the patient becomes pregnant while taking this drug, the patient should be warned of the potential hazard to the fetus In pregnant women with untreated or inadequately treated Graves’ disease, there is an increased risk of adverse events of maternal heart failure, spontaneous abortion, preterm birth, stillbirth and fetal or neonatal hyperthyroidism Because methimazole crosses placental membranes and can induce goiter and cretinism in the developing fetus, hyperthyroidism should be closely monitored in pregnant women and treatment adjusted such that a sufficient, but not excessive, dose be given during pregnancy Due to the rare occurrence of congenital malformations associated with methimazole use, it may be appropriate to use an alternative anti-thyroid medication in pregnant women requiring treatment for hyperthyroidism particularly in the first trimester of pregnancy during organogenesis. Given the potential maternal adverse effects of propylthiouracil (e.g., hepatotoxicity), it may be preferable to switch from propylthiouracil to methimazole for the second and third trimesters.

The appropriate treatment for a pregnant patient with hyperthyroidism is propylthiouracil during the first trimester, but it may be preferable to switch to methimazole for the second and third trimesters due to the potential maternal adverse effects of propylthiouracil 2 3.

• Key considerations:
  • Closely monitor hyperthyroidism in pregnant women
  • Adjust treatment to give a sufficient, but not excessive, dose during pregnancy
  • Consider alternative anti-thyroid medications, such as propylthiouracil, particularly during the first trimester
  • Be aware of the potential maternal adverse effects of propylthiouracil and the rare occurrence of congenital malformations associated with methimazole use.

From the Research

Treatment Options for Hyperthyroidism in Pregnancy

The patient's symptoms, including fatigue, sweating, and a diffuse enlargement of the thyroid gland, along with a positive urine pregnancy test and a thyroid-stimulating hormone level of zero, indicate hyperthyroidism in pregnancy.

• The appropriate treatment for hyperthyroidism in pregnancy is crucial to prevent complications for both the mother and the fetus.
• According to 4, propylthiouracil (PTU) is the preferred antithyroid drug for treatment of hyperthyroidism during pre-pregnancy months and the first 16 weeks of gestation due to its lower teratogenic effects compared to methimazole (MMI).
• 5 and 6 suggest that antithyroid medications, such as methimazole and propylthiouracil, can be used to treat hyperthyroidism, and the choice of treatment depends on the underlying diagnosis, presence of contraindications, severity of hyperthyroidism, and patient preference.
• 7 recommends that patients with hyperthyroidism should be treated with beta blockers for any cardiovascular manifestations and antithyroid medications to establish a euthyroid state before considering surgery.
• 8 states that methimazole and propylthiouracil are the main antithyroid drugs used for hyperthyroidism, with methimazole being the drug of choice due to its longer half-life and fewer severe side effects.

Initiation of Therapy

Given the patient's pregnancy status and the need to manage hyperthyroidism, initiation of therapy with propylthiouracil (PTU) would be an appropriate choice, considering its preferred use during the first 16 weeks of gestation 4.

• It is essential to monitor the patient's thyroid function tests and adjust the treatment as necessary to maintain a euthyroid state.
• The patient's cardiovascular manifestations, such as tachycardia, should also be managed with beta blockers as needed 7.