Which single feature most strongly favors ABO incompatibility rather than Rh isoimmunization as the cause of early neonatal jaundice?

• A Severe hydrops fetalis
• B Marked hepatosplenomegaly at birth
• C Strongly positive direct antiglobulin test on cord blood
• D Occurrence in a first pregnancy with no prior sensitizing event ✓

Explanation

Naturally occurring anti-A and anti-D are IgM antibodies present from the first pregnancy, so ABO hemolytic disease can occur in a firstborn without any preceding sensitization. ABO disease is usually mild, with spherocytes on smear and a weakly positive or even negative direct antiglobulin test, which kills option C. Profound anemia, hydrops and striking hepatosplenomegaly are hallmarks of Rh disease, where antibodies develop only after prior exposure.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.