**Core Concept**
In fetomaternal hemorrhage, it is crucial to differentiate between maternal and fetal blood to determine the extent of blood loss and the need for transfusion. This differentiation is essential for proper management and to avoid complications such as alloimmunization.

**Why the Correct Answer is Right**
The Kleihauer-Betke test is a widely used method to detect fetal hemoglobin in maternal blood, allowing for the differentiation between maternal and fetal blood. This test takes advantage of the resistance of fetal hemoglobin to acid elution, whereas adult hemoglobin is eluted from the red blood cells. By staining the blood smear with an acid-based stain, fetal hemoglobin-containing red blood cells remain intact, while adult hemoglobin-containing cells are eluted, making them appear pale or "ghost" cells.

**Why Each Wrong Option is Incorrect**
**Option A:** The Apt test is used to differentiate between fetal and adult hemoglobin, but it is not the primary test used in fetomaternal hemorrhage. It is more commonly used to differentiate between fetal and adult blood in newborns.
**Option B:** The Apt test is also not the correct answer as it is not used for this specific purpose.
**Option C:** The Kleihauer-Betke test is the correct answer, not Option C.
**Option D:** This option is not a valid test for differentiating between fetal and maternal blood.

**Clinical Pearl / High-Yield Fact**
In cases of suspected fetomaternal hemorrhage, it is essential to perform the Kleihauer-Betke test promptly to determine the extent of blood loss and to guide further management.

**Correct Answer: C. Kleihauer-Betke test**