**Core Concept**
The Rh D alloimmunization is a condition where a pregnant woman with Rh-negative blood develops antibodies against the Rh D antigen from her Rh-positive fetus, leading to hemolytic disease of the newborn (HDN). Diagnosing the fetal Rh genotype is crucial for determining the risk of HDN and for planning appropriate management.

**Why the Correct Answer is Right**
The non-invasive test used to diagnose fetal Rh genotype is **Maternal Plasma Cell-Free DNA (cfDNA) analysis**. This test involves analyzing the DNA present in the maternal bloodstream, which includes DNA from the fetus. By identifying the specific fetal Rh D alleles, the test can determine the fetal Rh genotype. This test is non-invasive, reliable, and can be performed early in pregnancy.

**Why Each Wrong Option is Incorrect**
* **Option A:** Amniocentesis - This is an invasive test that involves withdrawing a sample of amniotic fluid for genetic analysis. While it can diagnose fetal Rh genotype, it carries a risk of miscarriage and is not considered a non-invasive test.
* **Option B:** Chorionic villus sampling (CVS) - This is an invasive test that involves obtaining a sample of placental tissue for genetic analysis. Like amniocentesis, it carries a risk of miscarriage and is not considered a non-invasive test.
* **Option D:** Fetal blood sampling - This is an invasive test that involves directly sampling fetal blood for genetic analysis. It carries a significant risk of miscarriage and is not a routine diagnostic tool for fetal Rh genotype.

**Clinical Pearl / High-Yield Fact**
Maternal Plasma Cell-Free DNA analysis is a non-invasive test that can detect fetal Rh D alleles as early as 10 weeks of gestation, allowing for early identification of Rh D alloimmunization and timely management.

**Correct Answer:** C. Maternal Plasma Cell-Free DNA (cfDNA) analysis.