Most common antigen involved in erythroblastosis fetalis is –
## **Core Concept**
Erythroblastosis fetalis, also known as hemolytic disease of the newborn (HDN), occurs when there is an incompatibility between the blood types of a mother and her fetus. This incompatibility leads to the mother's immune system producing antibodies against the fetus's red blood cells, marking them for destruction. The most common antigens involved in this condition are those from the Rh blood group system.
## **Why the Correct Answer is Right**
The correct answer, **Rh(D) antigen**, is the most common antigen involved in erythroblastosis fetalis. This is because the Rh(D) antigen is highly immunogenic, and when an Rh-negative mother is exposed to Rh-positive blood (either during pregnancy, delivery, or a medical procedure), she may develop anti-Rh(D) antibodies. If she becomes pregnant with an Rh-positive fetus, these antibodies can cross the placenta and destroy the fetus's red blood cells, leading to hemolytic disease. The Rh(D) antigen is responsible for the majority of cases of erythroblastosis fetalis due to its high immunogenicity and the relatively high prevalence of Rh-positive individuals in the population.
## **Why Each Wrong Option is Incorrect**
- **Option A:** While other Rh antigens like RhCE (which includes C and E antigens) can also cause erythroblastosis fetalis, they are less commonly involved compared to the Rh(D) antigen.
- **Option B:** The Kell antigen can cause hemolytic disease of the newborn but is less common than Rh(D) antigen-related cases.
- **Option C:** ABO blood group incompatibility can cause hemolytic disease of the newborn, but it is typically milder and less common than Rh(D) incompatibility.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that administering Rh immune globulin (RhIg) to Rh-negative mothers at 28 weeks of gestation and within 72 hours of delivery (if the baby is Rh-positive) significantly reduces the risk of developing anti-Rh(D) antibodies and, consequently, the risk of erythroblastosis fetalis in future pregnancies.
## **Correct Answer:** . Rh(D) antigen