**Core Concept**
Fetal karyotyping involves analyzing the genetic material of the fetus, typically through amniocentesis or chorionic villus sampling. The volume of amniotic fluid required for karyotyping is critical to ensure accurate results while minimizing the risk of complications.

**Why the Correct Answer is Right**
A minimum of 5-10 mL of amniotic fluid is typically required for fetal karyotyping. This volume allows for the isolation of sufficient fetal cells for culture and analysis. The cells are then subjected to various biochemical and cytogenetic tests to identify any chromosomal abnormalities. The process involves the growth of cells in culture, followed by the application of techniques such as G-banding or fluorescent in situ hybridization (FISH) to analyze the chromosomes.

**Why Each Wrong Option is Incorrect**
**Option A:** 2 mL is insufficient for karyotyping, as it may not contain enough fetal cells for analysis. This could lead to inconclusive or inaccurate results.
**Option B:** 20 mL is excessive and increases the risk of complications, such as amniotic fluid leakage or fetal distress.
**Option C:** No volume specified is incorrect, as a specific volume of amniotic fluid is required for karyotyping to ensure accurate results.

**Clinical Pearl / High-Yield Fact**
When performing amniocentesis for fetal karyotyping, it is essential to collect at least 5-10 mL of amniotic fluid to ensure sufficient fetal cells for analysis, minimizing the risk of inconclusive or inaccurate results.

**Correct Answer:** C.