**Core Concept**
Prenatal diagnosis involves detecting and diagnosing fetal abnormalities during pregnancy using various techniques. At 16 weeks of gestation, several methods can be employed to assess fetal health and detect potential issues.

**Why the Correct Answer is Right**
At 16 weeks, ultrasound is a primary tool for prenatal diagnosis, allowing for accurate measurement of fetal size, detection of congenital anomalies, and assessment of fetal well-being. Amniocentesis, a procedure that involves withdrawing a small sample of amniotic fluid for genetic testing, can also be performed. Chorionic villus sampling (CVS) is another invasive prenatal diagnostic test, typically performed between 10 and 12 weeks of gestation, which samples placental tissue for genetic analysis.

**Why Each Wrong Option is Incorrect**
**Option A:**
Ultrasound is a widely used and safe diagnostic tool for prenatal assessment, especially at 16 weeks of gestation.

**Option B:**
Amniocentesis is a valid option for prenatal diagnosis at 16 weeks, providing valuable genetic information.

**Option C:**
Chorionic villus sampling (CVS) is typically performed earlier in pregnancy, between 10 and 12 weeks, making it less suitable for a 16-week prenatal diagnosis.

**Clinical Pearl / High-Yield Fact**
Key prenatal diagnostic milestones include:
- 10-12 weeks: Chorionic villus sampling (CVS)
- 16 weeks: Amniocentesis, ultrasound
- 20-22 weeks: Non-invasive prenatal testing (NIPT), ultrasound

**Correct Answer: C. Chorionic villus sampling (CVS) is typically performed earlier in pregnancy, between 10 and 12 weeks, making it less suitable for a 16-week prenatal diagnosis.**