## **Core Concept**
The triple test, also known as the triple screen or multiple marker test, is a prenatal screening test used to detect an increased risk of certain birth defects, particularly **Down syndrome** (Trisomy 21), **Trisomy 18**, and **neural tube defects**. It measures levels of certain substances in the maternal serum.

## **Why the Correct Answer is Right**
The triple test typically includes:
- **Alpha-fetoprotein (AFP)**: A protein produced by the fetus. Abnormal levels can indicate potential issues such as neural tube defects or Down syndrome.
- **Human chorionic gonadotropin (hCG)**: A hormone produced during pregnancy. Elevated levels can be associated with an increased risk of Down syndrome.
- **Unconjugated estriol (uE3)**: A form of estrogen produced by the fetus and placenta. Low levels can indicate Down syndrome or other fetal complications.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not specified, but if it refers to one of the commonly included markers (AFP, hCG, or uE3), it would not be the correct answer.
- **Option B:** Similarly, if this option refers to another commonly included marker, it would not be correct.
- **Option D:** This option is also not specified, but if it's one of the standard markers, it wouldn't be the right choice for "except."

## **Why Option C is Correct (Implicitly)**
Given that the question asks for "all of the following except," and without specific details on options A, B, C, and D, we infer based on common knowledge that **inhibin-A** is sometimes considered part of a quad screen test (which includes AFP, hCG, uE3, and inhibin-A) rather than the traditional triple test.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while the triple test can identify pregnancies at increased risk for certain conditions, it is not diagnostic. Positive results require further testing, such as amniocentesis or chorionic villus sampling (CVS), for a definitive diagnosis. The **quadruple screen** or **quad screen**, which adds inhibin-A to the markers tested, can provide a more accurate risk assessment.

## **Correct Answer: C.**