Which antithyroid medication is used in pregnancy?
**Core Concept**
The management of hyperthyroidism in pregnancy requires careful consideration of the safety and efficacy of antithyroid medications. **Propylthiouracil (PTU)** is a medication used to treat hyperthyroidism, particularly in pregnant women, due to its ability to cross the placenta and prevent fetal goiter.
**Why the Correct Answer is Right**
Propylthiouracil works by inhibiting the synthesis of thyroid hormones through the inhibition of **thyroid peroxidase (TPO)** and **type 5 5'-deiodinase (D5)** enzymes. This prevents the production of T3 and T4, thereby reducing thyroid hormone levels. In pregnancy, PTU is preferred over methimazole due to its lower risk of inducing **congenital anomalies**, such as aplasia cutis and choanal atresia.
**Why Each Wrong Option is Incorrect**
* **Option A:** Methimazole is associated with a higher risk of congenital anomalies and is generally avoided in pregnancy.
* **Option B:** Iodine is not an antithyroid medication and is used primarily to suppress thyroid hormone production in cases of thyroid storm or acute thyroiditis.
* **Option C:** Radioactive iodine is contraindicated in pregnancy due to the risk of **transplacental passage** and subsequent thyroid damage to the fetus.
**Clinical Pearl / High-Yield Fact**
It is essential to monitor thyroid function closely in pregnant women taking PTU, as well as to perform regular fetal ultrasounds to assess for any potential congenital anomalies.
**Correct Answer: C. Iodine is not an antithyroid medication and is used primarily to suppress thyroid hormone production in cases of thyroid storm or acute thyroiditis.**