**Core Concept**
Maternal serum alpha-fetoprotein (MSAFP) levels are used as a screening test for fetal abnormalities, particularly neural tube defects (NTDs) and abdominal wall defects. Elevated MSAFP levels can indicate an increased risk of NTDs or other fetal anomalies.

**Why the Correct Answer is Right**
An elevated MSAFP level indicates an increased risk of fetal anomalies, and further diagnostic testing is necessary to confirm the presence of a specific condition. Amniocentesis is a diagnostic test that involves withdrawing a sample of amniotic fluid from the uterus to assess fetal lung maturity, detect any infections, and diagnose chromosomal abnormalities or NTDs. This test is particularly useful in cases where MSAFP levels are elevated, as it can provide a definitive diagnosis and guide further management.

**Why Each Wrong Option is Incorrect**
* **Option A:** Ultrasound examination is a useful tool for screening fetal anomalies, but it does not provide a definitive diagnosis. It can help identify potential issues, but further testing is still required.
* **Option B:** Non-stress test (NST) is a screening test for fetal well-being, but it is not directly related to elevated MSAFP levels. It is used to assess fetal heart rate patterns and detect potential fetal distress.
* **Option D:** Chorionic villus sampling (CVS) is a diagnostic test that involves removing a sample of placental tissue to detect chromosomal abnormalities. While it is a useful test, it is not the most appropriate choice for elevated MSAFP levels.

**Clinical Pearl / High-Yield Fact**
Elevated MSAFP levels can be caused by various factors, including multiple gestations, fetal anomalies, and maternal conditions such as obesity or diabetes. A thorough medical and obstetric history, as well as a physical examination, is essential in evaluating the patient and determining the best course of action.

**Correct Answer: C. Amniocentesis. Amniocentesis is a diagnostic test used to confirm the presence of fetal anomalies in cases of elevated MSAFP levels.**