**Core Concept**
Alpha-fetoprotein (AFP) is a protein produced by the yolk sac and the fetal liver during pregnancy. It is a major plasma protein in the fetus and plays a crucial role in fetal development. Elevated levels of AFP can be indicative of certain fetal or maternal conditions.

**Why the Correct Answer is Right**
AFP levels are increased in conditions where there is an abnormal development of the fetus or an abnormality in the maternal-fetal interface. In most cases, elevated AFP levels are associated with conditions such as Down syndrome, neural tube defects, and certain types of cancer. **Option C** is a condition where AFP levels are typically decreased, not increased. This is because the placenta produces AFP, and in conditions like placental insufficiency, the placenta may not function properly, leading to decreased AFP levels.

**Why Each Wrong Option is Incorrect**
**Option A:** Not enough information is provided to determine if this condition is associated with increased AFP levels.
**Option B:** This condition is not typically associated with decreased AFP levels; however, more information is needed to confirm the relationship between this condition and AFP levels.
**Option D:** This condition is associated with increased AFP levels due to abnormal fetal development.

**Clinical Pearl / High-Yield Fact**
AFP levels can be used as a screening tool for certain fetal and maternal conditions. However, it is essential to note that a single abnormal result may not necessarily indicate a problem, as AFP levels can be influenced by various factors, including maternal health and fetal development.

**Correct Answer:** D.