## **Core Concept**
ABO incompatibility between a mother and her newborn can lead to hemolytic disease of the newborn (HDN), a condition where the mother's immune system produces antibodies against the ABO blood group antigens present on the newborn's red blood cells. This results in the destruction of the newborn's red blood cells. The condition is typically milder than Rh incompatibility and often does not require treatment.

## **Why the Correct Answer is Right**
The correct answer, , shows spherocytes, which are characteristic in cases of ABO incompatibility. Spherocytes are small, rounded red blood cells that have lost their biconcave disk shape. They are a result of the partial phagocytosis of red blood cells that have been opsonized (marked) by maternal antibodies. The presence of spherocytes on a peripheral blood smear is a hallmark of immune-mediated hemolysis, such as that seen in ABO incompatibility.

## **Why Each Wrong Option is Incorrect**
* **Option A:** - This option does not specifically relate to a characteristic finding in ABO incompatibility.
* **Option B:** - While nucleated red blood cells can be seen in various conditions of stress or prematurity, they are not specific for ABO incompatibility.
* **Option D:** - This option does not describe a typical finding in the context of ABO incompatibility.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that ABO incompatibility often results in a milder form of hemolytic disease of the newborn compared to Rh incompatibility. The presence of spherocytes on a peripheral smear is a critical diagnostic clue. It's also important to note that ABO incompatibility can occur in a mother with blood type O and a fetus with blood type A or B, as the mother can develop anti-A or anti-B antibodies.

## **Correct Answer:** . Spherocytes.