**Core Concept**
Lifestyle modifications and pharmacological interventions are crucial in managing hypertension during pregnancy. The choice of antihypertensive agent is critical due to potential fetal and maternal risks.

**Why the Correct Answer is Right**
Methyldopa is a centrally acting alpha-2 adrenergic agonist that is considered safe for use in pregnancy. It works by stimulating alpha-2 adrenergic receptors in the brain, leading to a decrease in sympathetic outflow and a subsequent reduction in blood pressure. Methyldopa is effective in controlling hypertension and is often used as a first-line treatment in pregnant women.

**Why Each Wrong Option is Incorrect**
**Option A:** Labetalol is a mixed alpha and beta blocker. While it is sometimes used in pregnancy, it is not the preferred first-line agent due to potential effects on fetal heart rate and growth.
**Option B:** Hydralazine is a vasodilator that can be used in pregnancy, but it is typically reserved for severe hypertension or acute management due to potential effects on fetal well-being.
**Option C:** Amlodipine is a calcium channel blocker that is generally avoided in pregnancy due to potential effects on fetal development.

**Clinical Pearl / High-Yield Fact**
Methyldopa is often used as a first-line treatment for hypertension in pregnancy due to its safety profile and effectiveness.

**Correct Answer: D. Methyldopa**