**Core Concept**
In pregnancy, certain antihypertensive medications can cause fetal harm or have adverse effects on maternal and fetal well-being. The choice of antihypertensive agent is critical during pregnancy, and certain drugs are contraindicated due to their potential risks.

**Why the Correct Answer is Right**
Methyldopa is an antihypertensive agent that acts by stimulating alpha-2 adrenergic receptors in the central nervous system, leading to decreased sympathetic outflow and vasodilation. While methyldopa is often used in pregnancy, it is not the correct answer because the question asks for a contraindicated drug. Methyldopa is generally considered safe during pregnancy, but it can cause fetal bradycardia and hypotension. However, the correct answer is a drug that is more clearly contraindicated in pregnancy.

**Why Each Wrong Option is Incorrect**
* **Option A:** Labetalol is a mixed alpha- and beta-blocker that is often used in pregnancy for hypertension. It is considered safe and effective for controlling blood pressure during pregnancy.
* **Option B:** Hydralazine is a vasodilator that is commonly used in pregnancy for acute hypertension. It is considered safe and effective for controlling blood pressure during pregnancy.
* **Option C:** Nifedipine is a calcium channel blocker that is often used in pregnancy for hypertension. It is considered safe and effective for controlling blood pressure during pregnancy.

**Clinical Pearl / High-Yield Fact**
When choosing an antihypertensive agent in pregnancy, consider the potential effects on fetal well-being and maternal cardiovascular stability. Drugs like methyldopa and labetalol are often used due to their safety profile, but it's essential to monitor fetal heart rate and maternal blood pressure closely.

**Correct Answer:** D.