**Core Concept**
Prenatal diagnosis at 16 weeks of pregnancy is a crucial aspect of maternal-fetal medicine, involving the evaluation of fetal health and development. This is typically achieved through various imaging modalities and biochemical markers.

**Why the Correct Answer is Right**
At 16 weeks of pregnancy, ultrasound is a primary tool for prenatal diagnosis. High-resolution ultrasound imaging allows for the assessment of fetal anatomy, including the detection of congenital abnormalities. The fetal nuchal translucency (NT) scan is a specific type of ultrasound that measures the thickness of the fluid-filled space at the back of the fetal neck. An increased NT thickness is associated with an elevated risk of chromosomal abnormalities, such as Down syndrome.

**Why Each Wrong Option is Incorrect**
* **Option A:** Amniocentesis is a prenatal diagnostic procedure that involves the withdrawal of amniotic fluid for genetic testing. However, it is typically performed between 15 and 20 weeks of gestation, and its primary purpose is to detect chromosomal abnormalities and fetal infections, not to perform a comprehensive fetal anatomy scan.
* **Option B:** Chorionic villus sampling (CVS) is another prenatal diagnostic procedure that involves the removal of a sample of placental tissue. CVS is usually performed between 10 and 12 weeks of gestation, earlier than the 16-week mark in question.
* **Option D:** Magnetic Resonance Imaging (MRI) is not typically used for routine prenatal diagnosis, especially at 16 weeks of gestation. While MRI can provide detailed images of fetal anatomy, it is often reserved for specific situations, such as suspected fetal anomalies or maternal conditions that may affect fetal development.

**Clinical Pearl / High-Yield Fact**
The nuchal translucency scan is a critical component of the first-trimester screening for Down syndrome, which also includes maternal serum markers and fetal nuchal fold thickness. A combination of these markers can provide a more accurate risk assessment for chromosomal abnormalities.

**Correct Answer: C. Ultrasound imaging, specifically the fetal nuchal translucency scan.**