A Rh-D negative woman delivers an Rh-D positive baby after an emergency cesarean for placental abruption with significant abruption estimated at 250 mL fetal blood exposure. Kleihauer-Betke (acid elution) test shows 2.8% fetal cells in maternal blood. The volume of fetomaternal hemorrhage (FMH) calculated using the Kleihauer-Betke result, assuming maternal blood volume of 5000 mL, is:

• A 140 mL fetal blood ✓
• B 70 mL fetal blood
• C 112 mL fetal blood
• D 56 mL fetal blood

Explanation

FMH volume = percentage fetal cells × maternal blood volume = 2.8% × 5000 mL = 140 mL. Each 30 mL of fetal whole blood (or 15 mL of fetal packed red cells) requires 300 mcg (1500 IU) of anti-D immunoglobulin. For 140 mL FMH: 140/30 = 4.67 vials → round up = 5 vials of 300 mcg = 1500 mcg (7500 IU) total anti-D required, administered as multiple doses with repeat KB test 48–72 hours after last injection to confirm clearance. The standard 300 mcg (1500 IU) post-delivery anti-D covers only 30 mL of FMH — this case requires supplemental dosing.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.