What are the recommendations for Rh immune globulin (RhIg) administration in an Rh-negative pregnant woman or woman of childbearing age?

Rh Immune Globulin (RhIg) Administration Recommendations

All Rh-negative pregnant women should receive RhIg at 28 weeks gestation and within 72 hours after delivery of an Rh-positive infant, as this two-dose protocol reduces alloimmunization rates from 12-13% down to 0.1-0.2%. 1, 2

Standard Prophylaxis Protocol for Pregnancy

Routine Antenatal and Postpartum Dosing

• Administer 300 μg RhIg at 28 weeks gestation to all unsensitized Rh-negative women when fetal blood type is unknown or known to be Rh-positive 1, 2, 3
• Administer 300 μg RhIg within 72 hours after delivery if the infant is Rh-positive 1, 2, 3
• The postpartum dose alone reduces alloimmunization from 12-13% to 1-2%, but adding the antenatal dose further reduces it to 0.1-0.2% 1, 3
• If RhIg is not given within 72 hours, administer as soon as recognized up to 28 days after delivery, as delayed administration still provides benefit 1, 4

Critical Eligibility Criteria

• The mother must be Rh-negative and not already sensitized to the Rh(D) antigen 3
• The infant must be Rh-positive (or blood type unknown) 3
• Women with "weak D" (Du-positive) should not receive RhIg 4

RhIg for Pregnancy Complications and Procedures

First Trimester Events (Before 12 Weeks)

• Administer 50 μg RhIg within 72 hours for spontaneous abortion, induced abortion, threatened abortion with heavy bleeding/pain, or ectopic pregnancy 1, 4
• If 50 μg dose is unavailable, use the standard 300 μg dose 1
• Fetal RBCs display Rh antigens from as early as 6 weeks gestation, making maternal sensitization possible even in very early pregnancy 1
• Fetomaternal hemorrhage occurs in 48% of threatened abortions, 36% of complete abortions, and 22% of incomplete abortions 1

Second and Third Trimester Events (After 12 Weeks)

• Administer 300 μg RhIg within 72 hours for: 1, 4
  • Spontaneous or induced abortion
  • Amniocentesis
  • Chorionic villus sampling
  • Cordocentesis
  • Ectopic pregnancy
  • Molar pregnancy (if partial mole or diagnosis uncertain)
  • External cephalic version attempts
  • Abdominal trauma
  • Placental or vaginal bleeding at any gestational age

Events Requiring Quantitative FMH Testing

• Consider quantitative testing for fetomaternal hemorrhage following events with significant placental trauma: 1, 4
  • Placental abruption
  • Blunt abdominal trauma (28% of pregnant patients with minor trauma have FMH)
  • Placenta previa with bleeding
  • Cordocentesis
• If FMH exceeds 15 mL of fetal RBCs (30 mL whole fetal blood), administer additional 10 μg RhIg per 0.5 mL of fetal RBCs beyond the standard dose 1, 4

Non-Pregnancy Indications

Transfusion of Rh-Positive Blood Products

• Administer RhIg to Rh-negative individuals who receive Rh-positive red blood cell transfusions to prevent alloimmunization 2, 3
• For Rh-negative women of childbearing potential receiving Rh-positive platelet transfusions, consider RhIg prophylaxis to prevent future pregnancy complications, though routine administration is not required for platelet transfusions due to minimal RBC content 2

Critical Timing and Dosing Considerations

Optimal Administration Window

• Within 72 hours of the sensitizing event is optimal for all indications 1, 2, 3, 4
• Administration up to 28 days post-event still provides benefit and is preferable to no administration 1, 4

Dose Selection by Gestational Age

• Before 12 weeks: 50 μg minimum (or 300 μg if 50 μg unavailable) 1, 4
• After 12 weeks: 300 μg standard dose 1, 4
• At 28 weeks gestation: 300 μg 1, 2
• Postpartum: 300 μg (or 120 μg with FMH testing) 1, 4

Common Pitfalls to Avoid

• Do not withhold RhIg based on early gestational age alone—fetal RBCs express D antigen from 6 weeks onward, making sensitization possible even in very early pregnancy 1, 2
• Do not assume minimal bleeding eliminates risk—even small amounts of fetomaternal hemorrhage can cause sensitization, and bleeding severity does not reliably predict hemorrhage volume 1
• Do not forget the postpartum dose if antenatal RhIg was given—both doses are essential for optimal protection 1, 3
• Verify blood type before withholding—if blood type is unknown and testing unavailable, administer RhIg if clinically indicated, as risks of administration are minimal compared to sensitization consequences 1, 2
• Do not administer RhIg to women who are already sensitized (have anti-D antibodies) or who are "weak D" positive 3, 4

Special Considerations

Paternity Testing

• When paternity is certain, Rh testing of the father may be offered to eliminate unnecessary RhIg administration if he is Rh-negative 4

Supply Shortages

• If RhIg supply is limited, prioritize postpartum patients and antenatal patients at later gestational ages 1
• Equivalent RhIg products may be substituted if the typically used brand is unavailable 1

Route of Administration

• Both intramuscular (IM) and intravenous (IV) routes are equally effective 5
• Choice depends on available preparations, dose requirements, and patient preference 5