Coagulation Disorders USMLE Step 1 Practice Question
A 29-year-old Rh-negative woman delivers her second child vaginally. She had elevated anti-D antibodies during pregnancy. The newborn presents with jaundice at 12 hours of life and poor feeding. Vital signs: HR 160/min, RR 45/min, Temp 37.2°C. Laboratory findings show hemoglobin 10.2 g/dL, reticulocyte count 8%, and elevated indirect hyperbilirubinemia. Direct antiglobulin test is positive. The infant has no petechiae or bleeding. Which mechanism best explains this clinical presentation?
Answer choices
- AMaternal IgM antibodies fix complement on fetal erythrocytes
- BLack of fetal intrinsic factor causes megaloblastic anemia
- CDefective fetal beta-globin synthesis causes intramedullary hemolysis
- DMaternal IgG antibodies cross the placenta and destroy fetal Rh-positive red blood cellsCorrect answer
- EFetal platelets are destroyed by anti-GpIIb/IIIa antibodies
- FMaternal IgG antibodies against fetal HLA antigens cause antibody-mediated cellular cytotoxicity of erythroid progenitors
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