**Core Concept**
Asymmetrical Intrauterine Growth Restriction (IUGR) is a condition where a fetus does not grow at a normal rate inside the womb, characterized by a discrepancy in growth between the head and the body. This is often due to placental insufficiency, leading to inadequate nutrient and oxygen supply to the fetus.

**Why the Correct Answer is Right**
In asymmetrical IUGR, the head is disproportionately affected due to the brain's high demand for oxygen and nutrients. The brain continues to grow, but the rest of the body lags behind, leading to a characteristic "head-sparing" effect. This is because the body prioritizes the growth of the brain, which is essential for fetal survival.

**Why Each Wrong Option is Incorrect**
**Option A:** Liver - Incorrect, as the liver is affected in asymmetrical IUGR, often showing signs of hepatosplenomegaly and fatty change.

**Option B:** Kidneys - Incorrect, as the kidneys are also affected, often showing signs of hypoplasia and dysfunction.

**Option C:** Pancreas - Incorrect, as the pancreas is affected, often leading to hypoglycemia due to inadequate insulin production.

**Clinical Pearl / High-Yield Fact**
In asymmetrical IUGR, the head-sparing effect is a key clinical feature, which can be used to differentiate it from symmetrical IUGR. Remember, in asymmetrical IUGR, the head grows normally, but the body lags behind.

**Correct Answer:** D