At what gestational age should RhoGAM (Rho(D) immune globulin) be administered to Rh-negative mothers?

RhoGAM Administration Timing During Pregnancy

RhoGAM should be administered to unsensitized Rh-negative women at 28 weeks' gestation, followed by another dose within 72 hours after delivery if the infant is Rh-positive. 1

Standard Administration Protocol

The recommended timing for RhoGAM administration follows a specific schedule:

1. Routine Antenatal Prophylaxis:

   • 300 mcg dose at 28 weeks' gestation 1, 2
   • Alternative: Two doses of 100-120 mcg (one at 28 weeks and one at 34 weeks) 3

2. Postpartum Administration:

   • 300 mcg within 72 hours after delivery of an Rh-positive infant 1, 2
   • If administration is delayed beyond 72 hours, RhoGAM should still be given up to 28 days after delivery 3

Special Circumstances Requiring RhoGAM

RhoGAM should also be administered in the following situations:

• Early Pregnancy Events (before 12 weeks' gestation):

  • 50 mcg (microdose) is typically adequate 1
  • 300 mcg if microdose is unavailable 1

• After 12 weeks' gestation:

  • 300 mcg for any potentially sensitizing event 3

• Specific Events Requiring Administration:

  • Spontaneous or induced abortion
  • Ruptured tubal pregnancy
  • Amniocentesis
  • Abdominal trauma
  • Chorionic villus sampling (120 mcg before 12 weeks, 300 mcg after 12 weeks) 3
  • Cordocentesis (300 mcg) 3

Duration of Protection

The 28-week timing for antenatal prophylaxis is critical as studies show:

• A single 300 mcg dose at 28 weeks provides protection through delivery in most cases 4
• However, in some women, detectable antibody levels may not persist until delivery 5
• A repeat dose is generally not required at 40 weeks if the initial dose was given at 28 weeks 3

Efficacy of Antenatal Administration

Research demonstrates that antenatal RhoGAM administration at 28 weeks:

• Is 88% effective in preventing Rh isoimmunization during pregnancy in Rh-negative primigravidas 4
• Reduces the incidence of Rh isoimmunization from approximately 1.6% to less than 0.1% when combined with postpartum administration 2

Common Pitfalls to Avoid

1. Failing to administer both doses: If RhoGAM is given antepartum, it is essential that the mother receive another dose after delivery of an Rh-positive infant 2

2. Confusing blood type with antibody status: This can lead to inappropriate RhoGAM administration 1

3. Administering to Rh-positive women: This is unnecessary and wastes a limited resource 1

4. Missing the window for maximum effectiveness: While RhoGAM is most effective within 72 hours of delivery or a sensitizing event, it should still be given up to 28 days after if the need is recognized late 3

5. Not adjusting dosage for large fetomaternal hemorrhage: Additional anti-D may be required for fetomaternal hemorrhage greater than 15 mL of fetal red blood cells 3

The evidence strongly supports that the 28-week gestational age timing for routine antenatal RhoGAM administration, followed by postpartum administration, provides optimal protection against Rh alloimmunization.