## **Core Concept**
Chorionic villus sampling (CVS) or chorionic villus biopsy is a prenatal test in which a sample of chorionic villi is removed from the placenta for testing. It is primarily used to detect chromosomal abnormalities and certain genetic disorders. The test is usually performed between 10 and 12 weeks of gestation.

## **Why the Correct Answer is Right**
The correct answer, , implies a condition or scenario where CVS is not typically performed. CVS is generally avoided in cases where there is a risk of procedure-related complications that could outweigh the benefits, such as active vaginal bleeding.

## **Why Each Wrong Option is Incorrect**
- **Option A:** CVS can be performed for genetic diagnosis in the first trimester, making it a valid indication.
- **Option B:** CVS is used for detecting chromosomal abnormalities like Down syndrome, which is a valid indication.
- **Option C:** This option is not provided, but typically, CVS is used for conditions that can be diagnosed through genetic testing.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that CVS is contraindicated in cases of active vaginal bleeding, as it may increase the risk of pregnancy loss. CVS provides valuable information about the fetus's genetic makeup early in pregnancy, which is crucial for decision-making.

## **Correct Answer: D. Active vaginal bleeding.**