**Core Concept**
The management of hyperthyroidism in pregnancy requires careful consideration of the risks and benefits of various medications. Propylthiouracil is a thionamide antithyroid drug that is commonly used in pregnancy due to its safety profile.

**Why the Correct Answer is Right**
Propylthiouracil works by inhibiting the synthesis of thyroid hormones and also blocks the peripheral conversion of T4 to T3. It is the preferred treatment for hyperthyroidism in pregnancy, particularly during the first trimester, due to its lower risk of hepatotoxicity compared to methimazole. The drug is effectively excreted by the kidneys, making dose adjustments necessary in cases of renal impairment.

**Why Each Wrong Option is Incorrect**
**Option A:** ACE inhibitors are contraindicated in pregnancy due to the risk of fetal renal damage and other adverse effects.
**Option B:** Aldosterone is a hormone involved in sodium and potassium balance, but it is not a medication used to treat hyperthyroidism.
**Option C:** Angiotensin receptor blockers (ARBs) are also contraindicated in pregnancy due to similar risks to ACE inhibitors.

**Clinical Pearl / High-Yield Fact**
When managing hyperthyroidism in pregnancy, it is essential to note that the recommended initial dose of propylthiouracil is 100-150 mg daily, divided into two or three doses, to minimize the risk of hepatotoxicity.

✓ Correct Answer: D. Propylthiouracil