## **Core Concept**
Chorionic villous sampling (CVS), also known as chronic villous sampling, is a prenatal test that involves removing a small sample of cells from the placenta for genetic testing. The test is primarily used to detect chromosomal abnormalities and certain genetic disorders. It is typically performed during the early stages of pregnancy.

## **Why the Correct Answer is Right**
The correct gestational age for performing CVS is usually between **10 to 12 weeks** of pregnancy. This period is chosen because the placental villi are well-developed, making it easier to obtain a sufficient sample for analysis. Performing CVS at this stage allows for early detection of potential genetic issues, which can be crucial for decision-making regarding the pregnancy.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because performing CVS too early (before 10 weeks) may not yield sufficient villous tissue for analysis and might increase the risk of complications.
- **Option C:** This option is incorrect because performing CVS too late (after 12 weeks) may still be possible but is generally less preferred compared to the optimal window of 10-12 weeks. The risks and the amount of tissue may not be as favorable.
- **Option D:** This option is likely much too late for a routine CVS, as the test is usually conducted in the first trimester.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that CVS can be performed through two main methods: transcervical and transabdominal. The **transcervical approach** involves inserting a catheter through the cervix to reach the placenta, while the **transabdominal approach** involves inserting a needle through the abdomen. Both methods have their indications and risks, and the choice depends on the placental location and patient factors.

## **Correct Answer:** . 10-12 weeks.