A term neonate has a serum bilirubin of 18 mg/dL at 36 hours of age. Direct Coombs test is positive. The mother is blood group O Rh-positive, and the infant is blood group A Rh-positive. The MOST likely cause of hemolytic jaundice is:
- A ABO incompatibility ✓
- B Rh incompatibility
- C G6PD deficiency
- D Hereditary spherocytosis
Correct answer: A. ABO incompatibility
Explanation
The mother is group O and the infant is group A — this creates ABO incompatibility, where maternal anti-A IgG antibodies (naturally occurring) cross the placenta and hemolyze fetal red cells. ABO incompatibility is the most common cause of immune hemolytic disease of the newborn in Rh-positive infants. The positive direct Coombs test confirms antibody-mediated hemolysis. Rh incompatibility requires the mother to be Rh-negative, which this mother is not.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.