The drug of choice for hypehyroidism in third trimester of pregnancy is;
**Core Concept**
The management of hyperthyroidism in pregnancy requires careful consideration to balance the risks of untreated thyroid disease with the potential risks of antithyroid medications to the fetus. In the third trimester, the primary goal is to control maternal symptoms while minimizing the risk of fetal hypothyroidism.
**Why the Correct Answer is Right**
Propranolol is a beta-blocker that effectively controls the adrenergic symptoms of hyperthyroidism, such as palpitations and tremors, without crossing the placenta. It is considered the drug of choice in the third trimester of pregnancy due to its safety profile and ability to manage maternal symptoms without affecting fetal thyroid function. Propranolol does not affect thyroid hormone levels or fetal growth, making it an ideal choice for managing hyperthyroidism in pregnant women.
**Why Each Wrong Option is Incorrect**
**Option A:** Methimazole is an antithyroid medication that can cross the placenta and cause fetal hypothyroidism, making it a less desirable choice in the third trimester.
**Option B:** Propylthiouracil (PTU) is another antithyroid medication that can also cross the placenta and has a higher risk of hepatotoxicity, making it a less preferred option in the third trimester.
**Option C:** Radioactive iodine is contraindicated in pregnancy due to its potential to cause fetal thyroid ablation and hypothyroidism.
**Clinical Pearl / High-Yield Fact**
Beta-blockers like propranolol are essential in managing the adrenergic symptoms of hyperthyroidism in pregnancy, and their use should be continued until the underlying thyroid disease is controlled.
**Correct Answer: B. Propylthiouracil (PTU) is typically used in the first trimester, and Propranolol is used in the third trimester.