Who Should Receive Rh Immunoglobulin (RhoGAM)
All Rh-negative, unsensitized pregnant women should receive RhIg prophylaxis at 28 weeks gestation and within 72 hours after delivery of an Rh-positive infant, as this reduces alloimmunization rates from 1.8% to 0.1-0.2%. 1
Core Candidates for RhIg Administration
Routine Antenatal and Postpartum Prophylaxis
- Rh-negative pregnant women at 28 weeks gestation should receive 300 μg RhIg when fetal blood type is unknown or known to be Rh-positive 1, 2
- An alternative dosing strategy is 100-120 μg at both 28 weeks and 34 weeks gestation 2
- Within 72 hours after delivery of an Rh-positive infant, all Rh-negative women should receive 300 μg RhIg 1, 2
- This two-dose protocol (antenatal plus postpartum) decreases alloimmunization from 13-17% down to 0.1-0.2% 1, 3
Early Pregnancy Loss and Complications
- Spontaneous or induced abortion at <12 weeks: Minimum 50 μg (or 120 μg) RhIg within 72 hours 1, 2
- Pregnancy loss after 12 weeks: 300 μg RhIg 2
- Ectopic pregnancy: 120 μg before 12 weeks; 300 μg after 12 weeks 2
- Molar pregnancy: RhIg should be given unless complete mole is certain (partial mole may contain fetal tissue) 2
Critical timing consideration: Fetal RBCs display Rh antigens as early as 6 weeks gestation, making maternal sensitization possible even in very early pregnancy 1, 3. This is a common pitfall—never withhold RhIg based solely on early gestational age 1.
Pregnancy Complications Requiring RhIg
Bleeding Events
- Any placental or vaginal bleeding at any gestational age in unsensitized Rh-negative women warrants RhIg 1
- For bleeding before 12 weeks: 50 μg minimum (or 300 μg if lower dose unavailable) 1
- Threatened abortion with heavy bleeding or abdominal pain, especially near 12 weeks 1
Invasive Procedures
- Amniocentesis: 300 μg RhIg 2
- Chorionic villus sampling: 120 μg before 12 weeks; 300 μg after 12 weeks 2
- Cordocentesis: 300 μg RhIg 2
Trauma and High-Risk Events
- Minor trauma in pregnancy: Consider RhIg, as 28% of pregnant patients with minor trauma demonstrate fetomaternal hemorrhage 1
- Events with potential placental trauma (placental abruption, blunt abdominal trauma, external cephalic version, placenta previa with bleeding): 300 μg RhIg plus quantitative testing for fetomaternal hemorrhage 2
- If fetomaternal hemorrhage exceeds 15 mL of fetal RBCs (30 mL fetal blood), give additional 10 μg RhIg per 0.5 mL of fetal red blood cells 2
Important Exclusions and Special Considerations
Who Should NOT Receive RhIg
- Women with "weak D" (Du-positive) should not receive RhIg 2
- Already sensitized Rh-negative women (those with existing anti-D antibodies) do not benefit from RhIg 1
Timing Flexibility
- If RhIg is not given within 72 hours, administer as soon as recognized, up to 28 days after delivery or sensitizing event 2
- A repeat antepartum dose at 40 weeks is generally not required if the 28-week dose was given on schedule 2
Testing Recommendations
- All pregnant women should be typed and screened for alloantibodies at first prenatal visit and again at 28 weeks 2
- Paternal Rh testing may be offered when paternity is certain to eliminate unnecessary RhIg administration 2
- Blood type and antibody screen should be done at abortion unless recent results are available 2
Prioritization During Shortages
If RhIg supply is limited, prioritize postpartum patients and antenatal patients at later gestational ages, as these represent the highest risk periods for sensitization 1. Equivalent RhIg products may be substituted if the usual brand is unavailable 1.
Mechanism and Rationale
As little as 0.1 mL of Rh-positive fetal cells can cause alloimmunization 3. Fetomaternal hemorrhage occurs in approximately 50% of all deliveries 3. Without prophylaxis, approximately 17% of Rh-negative women become immunized after pregnancy with an ABO-compatible, Rh-positive infant 3. The introduction of RhIg prophylaxis reduced fetal mortality from Rh hemolytic disease from 120 per 100,000 live births to 1.5 per 100,000 3.