A 3-day-old term neonate has serum bilirubin of 22 mg/dL (predominantly unconjugated). Blood group of mother is O-positive and baby is A-positive. Direct Coombs test is positive. Which characteristic DISTINGUISHES ABO hemolytic disease from Rh hemolytic disease in the neonate?
- A ABO hemolytic disease is more severe than Rh disease and causes hydrops fetalis more commonly
- B ABO hemolytic disease causes predominantly conjugated hyperbilirubinemia
- C ABO hemolytic disease can occur in a firstborn infant, unlike Rh disease which requires prior sensitization ✓
- D Intravenous immunoglobulin is contraindicated in ABO hemolytic disease
Correct answer: C. ABO hemolytic disease can occur in a firstborn infant, unlike Rh disease which requires prior sensitization
Explanation
ABO incompatibility can affect the first pregnancy because mothers with blood group O have naturally occurring anti-A and anti-B IgG antibodies (not requiring prior sensitization), unlike Rh disease where sensitization from a previous pregnancy or transfusion is necessary. ABO disease is generally milder than Rh disease and rarely causes hydrops fetalis. The hyperbilirubinemia is unconjugated. IVIG is actually used in severe ABO hemolytic disease to reduce the rate of hemolysis.
Reference: Ghai Essential Pediatrics, 10th ed.
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