What is the recommended administration protocol for Anti-D (Rho(D) immune globulin) injection in Rh-negative mothers?

Anti-D Injection Protocol for Rh-Negative Mothers

Rh-negative pregnant women should receive RhD immune globulin (RhIg) at 28 weeks gestation and within 72 hours after delivery of an Rh-positive infant, with additional doses required for specific pregnancy complications to prevent RhD alloimmunization. 1

Standard Prophylaxis Protocol

• A two-dose protocol is recommended for Rh-negative pregnant women: 300 μg RhIg at 28 weeks gestation and within 72 hours after delivery of an Rh-positive infant 1
• This protocol reduces the rate of RhD alloimmunization from approximately 1.8% to between 0.1% and 0.2% 1
• If paternity is certain, testing the baby's father for Rh status may eliminate unnecessary administration of RhIg 2
• Women with "weak D" (Du-positive) should not receive anti-D 2

Dosing for Pregnancy Complications

First Trimester Events (<12 weeks gestation)

• For spontaneous or induced abortion, ectopic pregnancy, or chorionic villus sampling: 50 μg RhIg within 72 hours 3, 1, 4
• If the 50 μg dose is unavailable, use the standard 300 μg dose 1

Second and Third Trimester Events (>12 weeks gestation)

• For amniocentesis, cordocentesis, other invasive procedures, spontaneous or induced abortion, intrauterine fetal death, external cephalic version attempts, abdominal trauma, or obstetric hemorrhage: 100-300 μg RhIg 1, 4

Administration Timing and Route

• RhIg should be administered as soon as possible after a sensitizing event, ideally within 72 hours 1, 2
• If not given within 72 hours, RhIg should still be administered up to 28 days after the event, though effectiveness may be reduced 2
• Both intramuscular (IM) and intravenous (IV) administration routes are equally effective 5
• Anti-D IgG concentrations differ between IV and IM routes up to 7 days post-administration but become similar after 2-3 weeks 5

Special Considerations

Fetomaternal Hemorrhage (FMH)

• For events with potential placental trauma (abruption, blunt abdominal trauma, placenta previa with bleeding), quantitative testing for FMH should be considered 1, 2
• If FMH exceeds the amount covered by the standard dose, additional RhIg should be given at 10 μg per 0.5 mL of fetal red blood cells 4, 6

First Trimester Abortion or Miscarriage

• Despite some guidelines suggesting RhIg may not be necessary before 12 weeks, the Society for Maternal-Fetal Medicine recommends offering RhD testing and RhIg administration for spontaneous and induced abortion at <12 weeks gestation 3, 1
• This recommendation is based on the fact that fetal RBCs display red cell antigens from as early as 6 weeks of gestation, making maternal sensitization possible even in early pregnancy 3, 1

Clinical Impact and Rationale

• Prevention of RhD alloimmunization is essential given its potential to cause hemolytic disease of the fetus and newborn in subsequent pregnancies 1, 7
• Without prophylaxis, approximately 13-17% of Rh-negative women delivering Rh-positive infants would develop anti-D antibodies 1
• The risks associated with RhIg administration are low compared to the potential benefits of preventing alloimmunization 1

Common Pitfalls to Avoid

• Failing to recognize that fetal RBCs display red cell antigens from as early as 6 weeks gestation, making maternal sensitization possible in early pregnancy 1
• Not administering RhIg for first trimester pregnancy losses or terminations due to misconceptions about risk 3
• Delaying administration beyond 72 hours, which may reduce effectiveness 2
• Not considering additional doses for significant fetomaternal hemorrhage 2, 4