What is the most common cause of neonatal unconjugated hyperbilirubinemia appearing within the first 24 hours of life?

Answer and explanation

Correct answer: D. Hemolytic disease of the newborn (Rh or ABO incompatibility)

  1. Step 1: Any jaundice appearing within the first 24 hours of life is considered pathological until proven otherwise.
  2. Step 2: The most frequent etiology is immune-mediated erythrocyte hemolysis due to maternal-fetal blood group incompatibility (ABO or Rh incompatibility), resulting in rapid breakdown of red cells and surge in unconjugated bilirubin.
Answer
Hemolytic disease of the newborn (Rh or ABO incompatibility).
Why not the others: 'Physiological jaundice' never appears in the first 24 hours (typically develops on days 2-4); 'Breast milk jaundice' typically arises after the first week of life; 'Biliary atresia' causes conjugated (direct) hyperbilirubinemia presenting at 2-6 weeks with acholic stools.

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