From the Guidelines
Rh-negative pregnant women should be screened for Rh antibodies at their first prenatal visit, again at 28 weeks gestation, and whenever there is a potentially sensitizing event. This approach is based on the most recent and highest quality evidence, which emphasizes the importance of early detection and prevention of Rh sensitization to minimize the risk of hemolytic disease of the newborn 1. The initial screening involves a blood test called an antibody screen or indirect Coombs test, and if the initial antibody screen is negative, Rh-negative women should receive Rh immune globulin (RhoGAM) prophylactically at 28 weeks gestation and again within 72 hours after delivery if the baby is Rh-positive. Some key points to consider when screening for Rh antibodies include:
- The sensitivity and specificity of cell-free DNA testing for Rh (D) are 97.2% and 96.8%, respectively, making it a reliable method for detecting the Rh (D) genotype 1.
- Maternal titers should be repeated serially every 4 weeks and then more frequently if they are found to be rising or with advancing gestational age to minimize the risk of unnecessary procedures.
- The use of Rh immune globulin (RhoGAM) prophylactically at 28 weeks gestation and again within 72 hours after delivery if the baby is Rh-positive can help prevent Rh sensitization and reduce the risk of hemolytic disease of the newborn. It is essential to note that while cell-free DNA testing for Rh (D) is clinically available in the United States, assays for other antigens such as c, E, and Kell are available in Europe, highlighting the need for continued research and development in this area 1. Overall, the screening schedule for Rh antibodies in Rh-negative pregnant women should prioritize early detection and prevention of Rh sensitization to minimize the risk of hemolytic disease of the newborn.
From the FDA Drug Label
To maintain protection throughout pregnancy, the level of passively acquired anti-Rho(D) should not be allowed to fall below the level required to prevent an immune response to Rh positive red cells. For antenatal prophylaxis, one full dose syringe of HyperRHO S/D Full Dose (1500 IU; 300 mcg) is administered at approximately 28 weeks’ gestation.
The best time to screen for Rh antibodies in Rh-negative pregnant women is at approximately 28 weeks’ gestation for antenatal prophylaxis, and within 72 hours after delivery if the baby is Rh positive 2.
- Key points:
- Administer one full dose syringe of HyperRHO S/D Full Dose at approximately 28 weeks’ gestation.
- Administer another full dose within 72 hours following delivery if the infant is Rh positive.
From the Research
Optimal Time for Screening Rh Antibodies
The optimal time to screen for Rh antibodies in Rh-negative pregnant women is a crucial aspect of preventing Rh alloimmunization. According to the available evidence:
- Screening for Rh antibodies should be performed at the first prenatal visit and again at 28 weeks of gestation 3, 4.
- Antenatal prophylaxis with Rh immune globulin is recommended at 28 weeks of gestation to prevent Rh isoimmunization during pregnancy or within 3 days after delivery 3, 5, 6.
- A second dose of Rh immune globulin may be given at 34 weeks of gestation, depending on the specific guidelines and protocols in place 3, 5.
- The detection of anti-D antibodies after antepartum injections of Rh immune globulin is generally limited to a period of 75-100 days after administration 7.
Key Considerations
Some key considerations in determining the optimal time for screening Rh antibodies include:
- The risk of Rh isoimmunization during pregnancy or within 3 days after delivery 6
- The effectiveness of antenatal prophylaxis with Rh immune globulin in preventing Rh isoimmunization 3, 5, 6
- The potential for false-positive results due to the detection of anti-D antibodies after antepartum injections of Rh immune globulin 7
- The importance of individualized care and consideration of specific patient factors, such as previous pregnancies and transfusions 3, 4