What is the standard postpartum prophylactic dose of anti‑D immune globulin (Rho(D) Ig) for an unsensitized Rh‑negative mother after delivery of an Rh‑positive infant?

Standard Postpartum Anti-D Dose

Administer 300 μg (1500 IU) of anti-D immune globulin intramuscularly within 72 hours of delivery to an unsensitized Rh-negative mother who delivers an Rh-positive infant. 1, 2

Dosing Protocol

The standard postpartum dose is:

• 300 μg (1500 IU) administered intramuscularly, preferably in the deltoid muscle 2
• Timing: Within 72 hours of delivery for optimal effectiveness 1, 2
• Never administer intravenously when using IM preparations 2
• Never administer to the neonate 2

Critical Timing Considerations

While 72 hours is the target window, delayed administration still provides benefit:

• Anti-D may still be given beyond 72 hours if the window is missed, as some protection is better than none 1, 2
• Administration up to 28 days postpartum is still recommended when the 72-hour window is missed 1
• The degree of protection decreases with delayed administration, but it remains preferable to no administration at all 1

Dose Modification for Large Fetomaternal Hemorrhage

One standard 300 μg dose covers up to 15 mL of fetal red blood cells (approximately 30 mL of fetal whole blood). 2, 3

When excessive fetomaternal hemorrhage is suspected:

• Perform quantitative testing (modified Kleihauer-Betke or flow cytometry) to determine the volume of fetal red cells in maternal circulation 2, 4
• Calculate additional doses: Divide the volume of fetal RBCs by 15 mL to determine the number of vials needed 2
• If the calculation results in a fraction, round up to the next whole number (e.g., if 1.4, give 2 vials) 2
• Additional dosing formula: Give 10 μg of anti-D for every additional 0.5 mL of fetal red blood cells beyond the initial 15 mL 1, 3

When to Suspect Large Fetomaternal Hemorrhage

Consider quantitative testing in these high-risk scenarios:

• Placental abruption 3
• Blunt abdominal trauma 3
• Manual removal of placenta 3
• Cesarean delivery 3
• Stillbirth 3

Special Circumstance: Recent Antenatal Dose

If delivery occurs within 3 weeks of the 28-week antenatal dose, the postpartum dose may be withheld unless there is evidence of fetomaternal hemorrhage exceeding 15 mL of red blood cells. 2 This recognizes that adequate anti-D levels may still be present from the recent antenatal administration.

Common Pitfalls to Avoid

• Do not skip postpartum anti-D even if the mother received antenatal prophylaxis at 28 weeks—both doses are required for optimal protection (reducing alloimmunization from 1.8% to 0.1-0.2%) 1
• Do not assume a standard dose is sufficient after traumatic delivery, cesarean section, or placental complications—always consider testing for excessive fetomaternal hemorrhage 3, 4
• Do not delay administration waiting for laboratory confirmation of infant blood type if it will exceed 72 hours—give anti-D empirically and it can be documented as unnecessary later if the infant is Rh-negative 1
• Do not confuse IM and IV preparations—verify the route specified on the product label, as IM products must never be given IV 2

Clinical Effectiveness

This two-dose protocol (28 weeks antenatal + postpartum) is highly effective:

• Postpartum anti-D alone reduces alloimmunization from 13-17% to 1-2% 1
• Adding the antenatal dose further reduces alloimmunization from 1.8% to 0.1-0.2% 1