What is the management for Rh incompatibility in pregnancy?

Management of Rh Incompatibility in Pregnancy

All unsensitized Rh-negative pregnant women should receive anti-D immunoglobulin (RhoGAM) prophylaxis to prevent Rh alloimmunization, which can cause hemolytic disease of the fetus and newborn in subsequent pregnancies. 1

Prophylactic Administration Schedule

Standard Prophylaxis

• Antenatal prophylaxis: 300 mcg (1500 IU) at approximately 28 weeks' gestation 2
• Postpartum prophylaxis: 300 mcg (1500 IU) within 72 hours after delivery if infant is Rh-positive 2
  • If delivery occurs within 3 weeks after the last dose, postpartum dose may be withheld unless there is a fetomaternal hemorrhage exceeding 15 mL of red blood cells 2

Special Circumstances Requiring Anti-D Administration

First Trimester Events

• Threatened abortion with continuing pregnancy: 300 mcg (1500 IU) 2
• Miscarriage, abortion, or ectopic pregnancy before 13 weeks' gestation: 50 mcg (250 IU) mini-dose may be used 2
• Miscarriage, abortion, or ectopic pregnancy at or beyond 13 weeks' gestation: 300 mcg (1500 IU) 2

Second and Third Trimester Events

• Amniocentesis (15-18 weeks or third trimester): 300 mcg (1500 IU) 2
• Abdominal trauma: 300 mcg (1500 IU) 2
• If administered at 13-18 weeks: Another dose should be given at 26-28 weeks 2

Dosage Adjustments for Large Fetomaternal Hemorrhage

When large fetomaternal hemorrhage (>15 mL of fetal red blood cells) is suspected:

1. Perform quantitative test (e.g., Kleihauer-Betke acid elution stain) 2
2. Calculate additional doses needed:
   • Divide red blood cell volume by 15 mL to determine number of syringes needed
   • Always round up to next whole number (e.g., if calculation yields 1.4, give 2 syringes) 2

Administration Route and Timing

• Route: Intramuscular injection, preferably in deltoid muscle or lateral thigh (avoid gluteal region due to sciatic nerve injury risk) 2
• Timing: Ideally within 72 hours of potential exposure to Rh-positive blood 2
• Late administration: Some protection may still be afforded if given beyond 72 hours, up to 13 days after exposure 3
• IV vs. IM: Both routes appear equally effective, with IV administration showing higher initial concentrations but similar levels after 2-3 weeks 4

Special Considerations

Evidence for Effectiveness

• Anti-D immunoglobulin reduces Rh alloimmunization incidence from 12-13% to 1-2% when given postpartum 2
• Two-dose regimen (antenatal at 28 weeks plus postpartum) further reduces incidence to less than 0.1% 2

Important Caveats

• Only unsensitized Rh-negative women (negative antibody screen) are eligible for RhoGAM 1
• RhoGAM should NEVER be administered intravenously or to neonates 2
• The half-life of IgG is 23-26 days, so protection levels should be maintained throughout pregnancy 2
• In supply shortages, prioritize postpartum patients and antenatal patients at later gestational ages 1

Monitoring

• Anti-D may be detectable for up to 75 days after administration in most women, with only 2.4% showing detectable levels between 76-95 days 5
• Detection of anti-D more than 100 days after RhoGAM administration should raise suspicion of alloimmunization 5

By following this management protocol, the risk of Rh alloimmunization can be significantly reduced, preventing hemolytic disease of the fetus and newborn in subsequent pregnancies, which can lead to severe fetal anemia, hydrops fetalis, and even fetal death.