## **Core Concept**
Amniocentesis is a prenatal test in which a small sample of **amniotic fluid** is withdrawn from the **amniotic sac** surrounding a developing fetus. This fluid contains **fetal cells** that can be cultured and analyzed for chromosomal abnormalities. The test is primarily used to detect genetic disorders such as Down syndrome.

## **Why the Correct Answer is Right**
The correct answer is . Amniocentesis to detect chromosomal abnormalities can indeed be performed as early as **15-16 weeks** of gestation. At this stage, there is a sufficient amount of amniotic fluid, and the risk of complications is relatively low. The procedure involves inserting a needle into the amniotic sac under ultrasound guidance to collect a sample of fluid. Fetal cells in the fluid are then cultured and analyzed for chromosomal abnormalities.

## **Why Each Wrong Option is Incorrect**
* **Option A:** . This is too early for a standard amniocentesis for chromosomal analysis because the amount of amniotic fluid may be insufficient, and the risk of complications might be higher.
* **Option B:** . While some studies and newer techniques might allow for earlier detection, traditionally, amniocentesis for chromosomal abnormalities is not routinely performed this early.
* **Option D:** . This is later than typically required for initial amniocentesis for chromosomal analysis, although amniocentesis can be performed later in pregnancy for other reasons.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while amniocentesis can detect chromosomal abnormalities, it is typically offered to women **over 35 years old** (or with other risk factors) due to the slightly increased risk of **fetal loss** associated with the procedure. The test provides definitive diagnosis of certain genetic conditions, which can guide parental decisions and preparation.

## **Correct Answer: C. 15-16 weeks.**