**Core Concept**
Intrauterine growth restriction (IUGR) refers to a condition where a fetus does not grow at a normal rate inside the womb. This can be caused by various factors, including maternal, placental, and fetal issues. IUGR can lead to preterm birth, low birth weight, and increased risk of neonatal morbidity and mortality.

**Why the Correct Answer is Right**
The correct answer will be the option that is not a known cause of IUGR. Each of the other options will be examined for its relevance to IUGR. The pathophysiology of IUGR involves impaired placental function, leading to inadequate nutrient and oxygen supply to the fetus.

**Why Each Wrong Option is Incorrect**
**Option A:** Maternal hypertension is a known cause of IUGR, as it can lead to placental insufficiency and reduced blood flow to the fetus.
**Option B:** Placental abruption is another cause of IUGR, as it involves the premature separation of the placenta from the uterus, leading to decreased blood flow and oxygenation to the fetus.
**Option D:** Fetal anemia, such as that caused by Rh incompatibility or parvovirus B19 infection, can also lead to IUGR due to decreased oxygen delivery to the fetus.

**Clinical Pearl / High-Yield Fact**
A key risk factor for IUGR is maternal smoking, which can lead to placental vascular changes and decreased fetal growth.

**Correct Answer: A. Maternal hypotension is not a known cause of IUGR; in fact, maternal hypertension is a more common cause.**