An Rh-negative unsensitized woman delivers an Rh-positive baby. The Kleihauer-Betke test shows a fetomaternal hemorrhage of 40 mL of fetal blood. Standard dose anti-D immunoglobulin (300 mcg IM) covers up to 30 mL of fetal blood. What is the CORRECT additional management?
- A No additional dose needed; standard dose is always sufficient
- B Give two additional 300 mcg doses of anti-D immunoglobulin
- C Give one additional 300 mcg dose of anti-D immunoglobulin ✓
- D Administer plasmapheresis to remove sensitizing antigens
Correct answer: C. Give one additional 300 mcg dose of anti-D immunoglobulin
Explanation
Each 300 mcg dose of anti-D immunoglobulin covers approximately 30 mL of fetal whole blood (or 15 mL of fetal red cells). A fetomaternal hemorrhage of 40 mL requires coverage for an additional 10 mL beyond the first dose, so one additional 300 mcg vial is administered. The Kleihauer-Betke acid elution test (or flow cytometry) quantifies the fetal cells in maternal blood to calculate additional anti-D requirement. Anti-D must be given within 72 hours of delivery.
Reference: Williams Obstetrics, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.