## Core Concept
Alpha-fetoprotein (AFP) is a major plasma protein produced by the yolk sac and the liver during fetal development. It serves as a tumor marker for certain cancers and a screening tool for fetal anomalies. Elevated levels of AFP are associated with various conditions.

## Why the Correct Answer is Right
Option correctly identifies a condition where AFP levels are not increased. Typically, AFP levels are elevated in conditions such as hepatocellular carcinoma, certain germ cell tumors (like yolk sac tumors), and during pregnancy in cases of open neural tube defects or multiple gestations.

## Why Each Wrong Option is Incorrect
* **Option A:** This condition is associated with increased AFP levels.
* **Option B:** This condition also shows elevated AFP levels.
* **Option C:** Similarly, this condition is linked with increased AFP levels.

## Clinical Pearl / High-Yield Fact
A significant clinical pearl is that decreased AFP levels during pregnancy are associated with an increased risk of Down syndrome (Trisomy 21), while increased levels are linked with neural tube defects.

## Correct Answer Line
**Correct Answer: D.**