Anti-D (RhIG) Dosage After Delivery

Who Receives It

Standard Postpartum Dose

• The standard 300 mcg (US) dose covers a fetomaternal hemorrhage (FMH) of up to 30 mL of fetal whole blood (or 15 mL of packed RhD-positive red cells).
• Katzung's Basic and Clinical Pharmacology (16th Ed.) confirms: "The usual dose of Rh(D) immune globulin is 2 mL IM, containing approximately 300 mcg anti-Rh(D) IgG."
• Creasy & Resnik's Maternal-Fetal Medicine states: "Current recommendations in North America indicate that 300 µg of RhIG should be administered within 72 hours of delivery."

Dose Calculation for Excessive Fetomaternal Hemorrhage (FMH)

1. Rosette test (qualitative screening): if negative → standard 300 mcg dose is sufficient.
2. If rosette test is positive → perform Kleihauer-Betke test or flow cytometry to quantify FMH.
3. Calculate FMH volume:
   • % fetal cells × 50 = volume of FMH in mL (based on standard 5 L maternal blood volume)
4. Calculate vials required:
   • FMH volume (mL) ÷ 30 = number of vials (each vial = 300 mcg)
   • Round up if fraction ≥ 0.5; add one extra vial as a safety buffer.

• FMH = 1% × 5000 mL = 50 mL
• Vials = 50 ÷ 30 = 1.67 → round up = 2 vials → +1 extra = 3 vials (900 mcg)

Large FMH / Extreme Doses

• No more than 5 vials (1500 mcg) IM in a 24-hour period due to volume constraints.
• If very large dose required (e.g., mismatched transfusion, 3rd trimester fetal demise): give IV in divided increments of maximum 600 mcg (3000 IU) every 8 hours.

Late Administration

• If inadvertently omitted: some protection is achieved up to 13 days post-delivery.
• Can be given up to 28 days post-delivery in guidelines - though this is suboptimal.

Important Notes

• One vial of RhIG suppresses immunization from 15 mL of RhD-positive packed RBCs.
• If delivery occurs <3 weeks after an antenatal RhIG dose (e.g., given for amniocentesis or ECV), a repeat dose is NOT required unless a large FMH is detected.
• RhIG is given to the mother, never to the infant.
• It is ineffective once alloimmunization to RhD has already occurred.

• Creasy & Resnik's Maternal-Fetal Medicine, Administration section
• Katzung's Basic and Clinical Pharmacology, 16th Ed., Rh(D) Immune Globulin
• Henry's Clinical Diagnosis and Management by Laboratory Methods, Prenatal/Postnatal Testing
• Quick Compendium of Clinical Pathology, 5th Ed., Prevention of Rh HDFN
• NHS Highland Anti-D Guidelines 2024 (UK: 500 IU for deliveries ≥20 weeks)