**Core Concept**
The question is testing knowledge of antihypertensive medications used in pregnancy, specifically the first-line treatment for hypertension in pregnant women. This involves understanding the safety profile and efficacy of various antihypertensive agents during pregnancy.

**Why the Correct Answer is Right**
Methyldopa is the antihypertensive of choice in pregnancy due to its long-standing safety record and effectiveness. It acts as a central alpha-2 adrenergic agonist, reducing sympathetic outflow to the heart, kidneys, and blood vessels. Methyldopa is considered safe for use in both mother and fetus, with a low risk of adverse effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Hydralazine is a vasodilator and is often used in acute hypertension in pregnancy, particularly in preeclampsia. However, it is not the first-line treatment for chronic hypertension.
**Option B:** Labetalol is a mixed alpha/beta-blocker and is used in pregnancy, especially when methyldopa is contraindicated or not tolerated. However, it is not the preferred initial treatment.
**Option C:** Nifedipine is a calcium channel blocker used in pregnancy, particularly for managing preeclampsia. It is not the first-line antihypertensive for chronic hypertension in pregnancy.

**Clinical Pearl / High-Yield Fact**
Methyldopa is often used in combination with other antihypertensive agents, such as diuretics, to manage resistant hypertension in pregnancy.

**Correct Answer: C. Methyldopa**