**Core Concept**
Amniocentesis is a prenatal diagnostic procedure that involves withdrawing a sample of amniotic fluid from the uterus to detect fetal abnormalities, including genetic disorders. This procedure is typically performed after 15 weeks of gestation and is considered a form of invasive prenatal testing.

**Why the Correct Answer is Right**
During amniocentesis, a small amount of amniotic fluid is aspirated from the uterus, which contains fetal cells that can be cultured and analyzed for chromosomal abnormalities, such as Down syndrome or other genetic disorders. The presence of specific genetic markers or chromosomal abnormalities can be detected through various laboratory tests, including karyotyping or fluorescence in situ hybridization (FISH). The amniotic fluid also contains alpha-fetoprotein (AFP), which can be measured to detect any potential neural tube defects or other congenital anomalies.

**Why Each Wrong Option is Incorrect**

* **Option A:** This option is incorrect because amniocentesis is not a form of non-invasive prenatal testing (NIPT), which involves analyzing cell-free DNA in the maternal blood to detect fetal abnormalities.
* **Option B:** This option is incorrect because amniocentesis is not a form of ultrasound, which uses high-frequency sound waves to produce images of the fetus.
* **Option C:** This option is incorrect because amniocentesis is not a form of chorionic villus sampling (CVS), which involves removing a sample of placental tissue to detect fetal abnormalities.

**Clinical Pearl / High-Yield Fact**
It's essential to note that amniocentesis carries a small risk of miscarriage, typically less than 1 in 300, and is usually recommended for women at high risk of carrying a fetus with a genetic disorder, such as those over 35 years old or with a family history of genetic disorders.

**Correct Answer: D. Invasive prenatal diagnostic procedure.**