**Core Concept:**
The question is asking about a method to distinguish between maternal and fetal blood components in a mixed blood sample. This is crucial in clinical situations where knowing the blood type or presence of certain substances in a baby's blood is necessary for proper management.

**Why the Correct Answer is Right:**
The correct answer, **D. Rhesus (Rh) typing**, is used to differentiate between maternal and fetal blood components. In Rhesus typing, antibodies (Rh antibodies) are identified in the maternal blood that can cross the placenta and potentially cause Rh isoimmunization or Rh disease in the fetus. This is a significant clinical issue in obstetrics, as it can lead to severe anemia and brain damage in the baby. By identifying the Rh typing, healthcare professionals can prevent or manage these complications effectively.

**Why Each Wrong Option is Incorrect:**
A. **Hemolysis** occurs when red blood cells break down, releasing hemoglobin into the plasma. Hemolysis cannot differentiate between maternal and fetal blood, as it is a general indicator of red blood cell destruction and not specific to either party.

B. **Blood grouping** refers to determining blood types (e.g., A, B, AB, O) but is not specific enough to differentiate between maternal and fetal blood.

C. **Fetal hemoglobin** is a form of hemoglobin present in a fetus's blood and can be used as a marker for fetal blood, but it cannot distinguish between maternal and fetal blood components in a mixed sample.

**Clinical Pearl / High-Yield Fact:**
In a clinical scenario, if Rh incompatibility is suspected, it is essential to immediately identify the Rh typing of both the mother and fetus. This information helps in implementing prophylactic measures, such as administering Rh immunoglobulin (RhIg) to the mother to prevent the development of Rh antibodies in the next pregnancy. Timely intervention is crucial in preventing Rh isoimmunization and its severe consequences in both the mother and fetus.