## **Core Concept**
Anencephaly is a severe form of neural tube defect (NTD) characterized by the absence of a major portion of the brain, skull, and scalp. It results from the failure of neural tube closure during embryonic development. Early detection of anencephaly is crucial for pregnancy management.

## **Why the Correct Answer is Right**
Anencephaly can be detected as early as 10-14 weeks of gestation through ultrasound examination. This is because the anomaly involves a significant structural defect that can be visualized with advancing gestational age and improving ultrasound technology. By 10-14 weeks, the anatomy of the fetus can be adequately assessed to identify the absence of the cranial vault.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 6 weeks - This is too early for a definitive diagnosis of anencephaly through ultrasound. While some fetal structures can be seen, the detailed anatomy required to diagnose anencephaly may not be fully assessable.
- **Option B:** 8 weeks - Similar to option A, 8 weeks might still be early for a detailed assessment of the fetal anatomy to confirm anencephaly.
- **Option D:** 20 weeks - Although anencephaly can certainly be diagnosed by 20 weeks, waiting until this gestational age may delay diagnosis and potential management options.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that anencephaly is associated with elevated levels of alpha-fetoprotein (AFP) on maternal serum screening. However, for definitive diagnosis, ultrasound is the preferred method. Early detection allows for informed decision-making regarding pregnancy management.

## **Correct Answer:** . 10-14 weeks