Management of Rh-Positive Pregnant Women
Rh-positive pregnant women do not require RhIg (Rho(D) immune globulin) prophylaxis, as they cannot develop anti-D alloimmunization from carrying an Rh-positive fetus. 1
Understanding the Rh System
The fundamental principle is straightforward: RhIg prophylaxis is designed exclusively for Rh-negative women to prevent alloimmunization when exposed to Rh-positive fetal blood cells. 1, 2
- Rh-positive women (those with the D antigen on their red blood cells) cannot form anti-D antibodies against Rh-positive fetal cells because they already possess this antigen. 2
- The fetal RhD antigen develops as early as 6 weeks gestation, making maternal sensitization physiologically possible only in Rh-negative mothers carrying Rh-positive fetuses. 1
Standard Prenatal Care for Rh-Positive Women
All pregnant women, regardless of Rh status, should undergo blood typing and antibody screening at the first prenatal visit and again at 28 weeks. 2
- This screening detects clinically significant antibodies beyond anti-D, including anti-Kell, anti-c, anti-E, and other red cell antibodies that can cause hemolytic disease of the fetus and newborn. 2
- If antibodies are detected in an Rh-positive woman, management depends on the specific antibody identified and requires specialist consultation. 3
Special Considerations for Antibody-Positive Rh-Positive Women
If an Rh-positive pregnant woman has positive antibody screening, the clinical approach differs entirely from Rh alloimmunization management:
Autoimmune Antibodies (Anti-Ro/SSA, Anti-La/SSB)
- Hydroxychloroquine should be continued throughout pregnancy to reduce the risk of congenital heart block in fetuses exposed to maternal anti-Ro/SSA or anti-La/SSB antibodies. 3
- Serial fetal echocardiography starting at 16-18 weeks and continuing through week 26 is mandatory for monitoring cardiac conduction abnormalities. 3
- If first- or second-degree heart block is detected, oral dexamethasone 4 mg daily is recommended, but should not be continued beyond several weeks due to fetal and maternal toxicity risks. 3
- Complete heart block should not be treated with dexamethasone, as it does not improve outcomes and causes harm. 3
Antiphospholipid Antibodies
- For obstetric antiphospholipid syndrome: Combined low-dose aspirin and prophylactic-dose low molecular weight heparin throughout pregnancy, with consideration of adding hydroxychloroquine. 3
- For thrombotic antiphospholipid syndrome: Therapeutic-dose low molecular weight heparin and low-dose aspirin throughout pregnancy and postpartum. 3
Critical Pitfalls to Avoid
- Do not confuse "weak D" (Du-positive) with Rh-negative status. Women with weak D phenotype should be considered Rh-positive and do not require RhIg. 2, 4
- Do not assume Rh-positive status eliminates all antibody-related risks. Other clinically significant antibodies can cause fetal hemolytic disease and require different management strategies. 2
- Do not administer RhIg to Rh-positive women, as this represents unnecessary blood product exposure without clinical benefit. 2