A term neonate develops jaundice at 30 hours of life. Total serum bilirubin (TSB) is 14 mg/dL. Blood group of mother is O positive; baby is A positive. Direct Coombs test (DCT) is positive. Which of the following statements about this condition is CORRECT?
- A This is Rh incompatibility; anti-D antibodies are responsible
- B This is ABO incompatibility; anti-A IgG antibodies cross the placenta; DCT may be weakly positive ✓
- C This is ABO incompatibility; it occurs only in O-positive mothers with A or B babies
- D This cannot be ABO incompatibility because Rh status is positive in the mother
Explanation
ABO hemolytic disease of the newborn (ABO HDN) occurs when an O blood group mother carries an A or B baby. O group individuals naturally possess anti-A and anti-B IgG antibodies (unlike A or B groups who predominantly have IgM), which can cross the placenta and coat fetal red cells, causing hemolysis. The DCT (direct Coombs) is positive but often weakly so in ABO HDN due to the lower density of A/B antigens on fetal RBCs. Jaundice within 24–48 hours is characteristic of immune hemolysis. Rh incompatibility involves anti-D IgG and is not relevant here since the mother is Rh-positive. ABO incompatibility can occur regardless of Rh status.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.