## **Core Concept**
The triple test, also known as the triple screen or Kettering test, is a screening test used during pregnancy to detect potential fetal abnormalities, specifically Down syndrome. It measures levels of certain substances in a pregnant woman's blood.

## **Why the Correct Answer is Right**
The triple test for Down syndrome involves measuring three substances in the maternal serum:
- **Alpha-fetoprotein (AFP)**,
- **Human chorionic gonadotropin (hCG)**, and
- **Unconjugated estriol (uE3)**.
These markers are used to assess the risk of Down syndrome in the fetus. Inhibin-A is actually part of the **quadruple screen test**, not the triple test.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Alpha-fetoprotein (AFP) is a part of the triple test.
- **Option B:** Human chorionic gonadotropin (hCG) is also a component of the triple test.
- **Option C:** Unconjugated estriol (uE3) is another component of the triple test.

## **Why Option D is Correct**
- **Option D:** Inhibin-A is not part of the triple test but is included in the **quadruple screen test** (also known as the quad screen), which is an extension of the triple test.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that while the triple test provides a risk assessment for Down syndrome, it is not diagnostic. A positive result indicates a higher risk but necessitates further diagnostic testing, such as amniocentesis.

## **Correct Answer:** D. Inhibin-A.