Which blood type requires an Rhogam (Rho(D) immune globulin) shot, specifically in pregnant women?

Which Blood Type Requires RhIg (Rhogam)?

Rh-negative (D-negative) pregnant women require RhIg prophylaxis to prevent RhD alloimmunization when carrying or potentially carrying an Rh-positive fetus. 1, 2

Blood Type Specifics

• Rh-negative women are the only candidates for RhIg administration 1, 3
• Women who are "weak D" (Du-positive) should NOT receive RhIg as they are considered Rh-positive for clinical purposes 3
• Women with molecularly defined Asian-type DEL (c.1227G>A) do not require RhIg, as they do not form alloanti-D when exposed to D-positive red cells 4
• Similarly, women with weak D types 1,2,3,4.0, and 4.1 do not need RhIg prophylaxis 4

Standard Prophylaxis Protocol

Timing and dosing:

• At 28 weeks gestation: Administer 300 mcg (1500 IU) RhIg to all unsensitized Rh-negative women when fetal blood type is unknown or known to be Rh-positive 1, 5
• Within 72 hours after delivery: Give 300 mcg (1500 IU) if the infant is Rh-positive 1, 5
• This two-dose protocol reduces alloimmunization rates from approximately 1.8% to between 0.1% and 0.2% 1

Additional Indications for RhIg in Rh-Negative Women

First trimester events (<12 weeks):

• Spontaneous or induced abortion: 50 mcg minimum dose (or 300 mcg if 50 mcg unavailable) 1, 5
• Ectopic pregnancy: 120 mcg minimum 3
• Threatened abortion with heavy bleeding or abdominal pain 1

After 12 weeks gestation:

• Miscarriage or abortion: 300 mcg 5, 3
• Amniocentesis: 300 mcg 5, 3
• Chorionic villus sampling: 300 mcg 3
• Cordocentesis: 300 mcg 3
• Abdominal trauma: 300 mcg 5, 3
• Placental bleeding or abruption: 300 mcg 1, 3

Dose Adjustments for Large Fetomaternal Hemorrhage

Critical consideration: One standard 300 mcg dose covers up to 15 mL of fetal red blood cells (approximately 30 mL of whole fetal blood) 5

• If fetomaternal hemorrhage exceeds 15 mL of fetal RBCs, perform quantitative testing (modified Kleihauer-Betke test) 5, 3
• Calculation: Divide the volume of fetal RBCs by 15 mL to determine the number of 300 mcg doses required 5
• If the calculation results in a fraction, round up to the next whole number (e.g., if 1.4, give 2 doses) 5
• For excess hemorrhage, give an additional 10 mcg per 0.5 mL of fetal red blood cells beyond the standard dose coverage 3

Critical Timing Window

The 72-hour window is essential but not absolute:

• RhIg is most effective when given within 72 hours of exposure 2, 5
• If not given within 72 hours, administer as soon as recognized, up to 28 days after the sensitizing event 3
• Delayed administration provides less protection but is still preferable to no administration 1

Common Pitfalls to Avoid

• Do not assume early pregnancy is safe: Fetal RBCs display D-antigens from as early as 6 weeks gestation, making sensitization possible even in first trimester 1, 2
• Do not withhold for "minimal" bleeding: Even small volumes (0.03-0.1 mL) of Rh-positive RBCs can trigger alloimmunization 2
• Do not give RhIg to women who are already sensitized (those with detectable anti-D antibodies) as it provides no benefit 1
• Do not administer to the neonate - RhIg is only given to the mother 5
• Do not inject intravenously when using IM preparations 5

Screening Requirements

• All pregnant women should have blood type and antibody screening at the first prenatal visit and again at 28 weeks 3
• When paternity is certain, testing the father's Rh status can eliminate unnecessary RhIg administration if he is Rh-negative 3