What are the guidelines for managing an Rh (Rhesus) negative pregnancy?

Management Guidelines for Rh Negative Pregnancy

Rh negative pregnant women should receive RhD immune globulin (RhIg) prophylaxis at 28 weeks gestation and within 72 hours after delivery of an Rh positive infant to prevent RhD alloimmunization and reduce the risk of hemolytic disease of the fetus and newborn in subsequent pregnancies. 1, 2

Standard RhIg Prophylaxis Protocol

• All unsensitized Rh negative pregnant women should be given RhIg 300 μg IM at 28 weeks gestation when fetal blood type is unknown or known to be Rh positive 3
• A postpartum dose of RhIg 300 μg IM should be administered within 72 hours of delivery to Rh negative women who deliver an Rh positive infant 2
• This two-dose protocol (antepartum and postpartum) reduces the rate of RhD alloimmunization from approximately 1.8% to between 0.1% and 0.2% 1
• If RhIg is not given within 72 hours of delivery, it should still be administered up to 28 days after delivery, although effectiveness may be reduced 3

RhIg Administration for Pregnancy Complications

• First trimester pregnancy loss (<12 weeks): Despite varying guidelines, the Society for Maternal-Fetal Medicine (SMFM) recommends offering both RhD testing and RhIg administration for spontaneous and induced abortion at <12 weeks gestation in unsensitized Rh negative individuals 1
• Dose for early pregnancy loss: 50 μg RhIg within 72 hours is adequate for first trimester losses; if unavailable, the standard 300 μg dose should be used 1
• Ectopic pregnancy: RhIg should be administered to unsensitized Rh negative women following ectopic pregnancy (minimum 120 μg before 12 weeks gestation) 3
• Threatened abortion: While some authorities consider RhIg unnecessary for threatened abortion with a viable fetus before 12 weeks, it is prudent to administer RhIg when there is heavy bleeding, abdominal pain, or when the event occurs near 12 weeks 1
• Abdominal trauma: Consider RhIg administration in cases of minor trauma in Rh negative patients, as 28% of pregnant patients with minor trauma have been shown to have fetomaternal hemorrhage 1

Invasive Procedures During Pregnancy

• Amniocentesis: RhIg 300 μg should be given to unsensitized Rh negative women following amniocentesis 3
• Chorionic villus sampling: RhIg should be given (minimum 120 μg during first 12 weeks, 300 μg after 12 weeks) 3
• Cordocentesis: RhIg 300 μg should be administered to unsensitized Rh negative women 3

Testing Recommendations

• All pregnant women should be typed and screened for alloantibodies with an indirect antiglobulin test at the first prenatal visit and again at 28 weeks 3
• When paternity is certain, Rh testing of the baby's father may be offered to eliminate unnecessary blood product administration 3
• Quantitative testing for fetomaternal hemorrhage (FMH) may be considered following events potentially associated with placental trauma (e.g., placental abruption, blunt trauma, cordocentesis) 3

Special Considerations

• Women with "weak D" (Du-positive) should not receive RhIg 3
• If RhIg supply is limited, postpartum patients and antenatal patients at later gestational ages should be prioritized 1
• A repeat antepartum dose of RhIg is generally not required at 40 weeks if the antepartum injection was given no earlier than 28 weeks gestation 3

Effectiveness and Outcomes

• Postpartum RhIg decreases the rate of anti-D alloimmunization from 13-17% to 1-2% 1, 2
• Adding the antenatal dose at 28 weeks further reduces alloimmunization from 1.8% to 0.1-0.2% 1
• Administration of RhIg has dramatically decreased the incidence of hemolytic disease of the fetus and newborn, significantly reducing perinatal morbidity and mortality 4, 5

Common Pitfalls to Avoid

• Failure to administer RhIg when indicated or in the appropriate dose is the most common reason for continued instances of Rh immunization 4
• Not recognizing that fetal RBCs display red cell antigens from as early as 6 weeks gestation, making maternal sensitization possible in early pregnancy 1
• Overlooking the need for RhIg after early pregnancy loss, which can lead to sensitization affecting future pregnancies 1, 3
• Delaying administration beyond 72 hours, which reduces effectiveness (though administration up to 28 days post-delivery is still recommended) 3

The evidence clearly demonstrates that proper administration of RhIg has been one of the most successful immunoprophylaxis programs in medicine, dramatically reducing the incidence of hemolytic disease of the fetus and newborn and its associated morbidity and mortality.