**Core Concept**
In pregnancy, certain anti-hypertensive medications pose significant risks to the fetus, necessitating careful selection of antihypertensive agents. Angiotensin-converting enzyme (ACE) inhibitors are one such class of medications that can cause fetal harm.

**Why the Correct Answer is Right**
ACE inhibitors, such as lisinopril and enalapril, work by blocking the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor. In pregnancy, this blockade can lead to decreased placental perfusion and fetal growth restriction. Furthermore, ACE inhibitors can cause oligohydramnios, a condition characterized by decreased amniotic fluid volume, which can lead to fetal renal damage and pulmonary hypoplasia. These effects are particularly concerning during the second and third trimesters of pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** Beta blockers, such as propranolol and atenolol, are often used to control hypertension in pregnancy, particularly in the context of pre-eclampsia. They work by reducing cardiac output and peripheral resistance.
**Option C:** Methyldopa is a centrally acting anti-adrenergic agent that is commonly used to treat hypertension in pregnancy. It is considered safe for use in pregnant women and is often used as a first-line treatment.
**Option D:** Calcium channel blockers, such as nifedipine and verapamil, are also used to control hypertension in pregnancy. They work by relaxing vascular smooth muscle and reducing peripheral resistance.

**Clinical Pearl / High-Yield Fact**
ACE inhibitors should be avoided in pregnancy, particularly during the second and third trimesters, due to the risk of fetal renal damage and pulmonary hypoplasia.

**✓ Correct Answer: B. ACE inhibitors**