Bart’s hydrops fetalis is lethal because
**Core Concept**
Bart's hydrops fetalis is a severe form of hemolytic disease of the newborn caused by Rh incompatibility between the mother and the fetus. This condition occurs when the mother has Rh-negative blood and the fetus has Rh-positive blood, leading to the production of antibodies against the Rh-positive blood cells.
**Why the Correct Answer is Right**
The correct answer is due to the severe anemia and hemolysis caused by the destruction of Rh-positive red blood cells by the maternal immune system. This results in a significant decrease in fetal hemoglobin, leading to cardiac failure and hydrops fetalis. The fetal heart is unable to pump blood effectively due to the severe anemia, resulting in fluid accumulation in the fetal tissues and organs, which is fatal.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while anemia is a contributing factor to the development of hydrops fetalis, it is not the sole cause. The correct answer highlights the specific mechanism of Rh incompatibility leading to hemolysis.
**Option B:** This option is incorrect because while cardiac failure is a consequence of the severe anemia, it is not the primary reason for the lethality of Bart's hydrops fetalis.
**Option C:** This option is incorrect because while fluid accumulation in the fetal tissues and organs is a characteristic of hydrops fetalis, it is not the underlying cause of the condition.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that Bart's hydrops fetalis is almost always fatal due to the severe anemia and cardiac failure, and it is essential to diagnose and manage Rh incompatibility promptly to prevent this condition.
**Correct Answer: D.**