Anomaly scan is done at _______ weeks of gestation

**Core Concept**
Anomaly scan, also known as detailed ultrasound scan, is a prenatal diagnostic test performed to detect fetal abnormalities and anomalies. This scan is typically done between 16 to 22 weeks of gestation, when the fetus is fully formed but still small enough to be visualized in detail.

**Why the Correct Answer is Right**
The correct answer is between 16 to 22 weeks of gestation because this period allows for a thorough evaluation of fetal anatomy, including the heart, brain, and limbs. At this stage, the fetus is too large to be visualized in detail before 16 weeks, and after 22 weeks, the risk of miscarriage increases, making it less ideal for detailed scanning. The scan is performed using high-frequency ultrasound waves, which can detect even the smallest abnormalities in fetal development.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too early for a detailed anomaly scan. Before 16 weeks, the fetus is too small and the ultrasound images are not clear enough for a thorough evaluation.
**Option B:** This option is incorrect because it is too late for a detailed anomaly scan. After 22 weeks, the risk of miscarriage increases, and the fetus may be too large to be visualized in detail.
**Option C:** This option is incorrect because it is not a standard time for an anomaly scan. While some scans may be performed earlier or later than 16 to 22 weeks, this is not the recommended time for a detailed anomaly scan.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the optimal time for an anomaly scan is between 16 to 22 weeks of gestation, as this allows for the best visualization of fetal anatomy and the detection of potential abnormalities.

**Correct Answer:** 20. 20 weeks of gestation