**Core Concept**
Methyldopa is a centrally acting antihypertensive agent that works by stimulating alpha-2 adrenergic receptors in the brain, leading to a decrease in sympathetic outflow and subsequently lowering blood pressure.

**Why the Correct Answer is Right**
Methyldopa is considered the drug of choice for hypertension in pregnancy due to its long-standing safety profile and efficacy in managing blood pressure. It has been used for decades and has a well-established track record in pregnant women, making it a preferred choice over other antihypertensive agents. Methyldopa can be used throughout pregnancy, including during the first trimester, and has not been associated with significant fetal harm.

**Why Each Wrong Option is Incorrect**
**Option A:** Hydralazine is a vasodilator that can be used to manage acute hypertension in pregnancy, but it is not the first-line treatment due to its potential for fetal distress and the need for frequent monitoring.
**Option C:** Labetalol is a mixed alpha and beta-blocker that can be used in pregnancy, but it is not the preferred choice due to its potential for fetal growth restriction and the need for close monitoring of fetal heart rate.
**Option D:** Nifedipine is a calcium channel blocker that can be used to manage hypertension in pregnancy, but it is not the first-line treatment due to its potential for fetal heart rate abnormalities and the need for close monitoring.

**Clinical Pearl / High-Yield Fact**
Methyldopa is unique in that it can be used to manage hypertension in pregnancy without crossing the placenta, making it a safe choice for the fetus. This is due to its ability to stimulate alpha-2 adrenergic receptors in the brain, which leads to a decrease in sympathetic outflow and subsequently lowers blood pressure.

**✓ Correct Answer: B. Methyldopa**