A standard dose of anti-D immunoglobulin (300 micrograms) administered after a sensitising event in an unsensitised Rh-negative woman suppresses immunisation against a fetomaternal haemorrhage of approximately:

• A 15 mL of fetal whole blood
• B 30 mL of fetal whole blood ✓
• C 60 mL of fetal whole blood
• D 120 mL of fetal whole blood

Explanation

Three hundred micrograms of anti-D clears approximately 30 mL of fetal whole blood, equivalent to 15 mL of fetal red cells, which is why larger bleeds require additional doses calculated from the Kleihauer-Betke estimate. Fifteen mL refers to packed cells, not whole blood, and 60 mL would need a doubled dose. This conversion is the basis for anti-D dose calculations in FMGE and NEET PG examinations.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.