From the Guidelines
This situation is good for the patient, as she is Rh negative and her antibody screen is negative for Rh antibodies, indicating she has not developed antibodies against the Rh factor despite not receiving RhoGAM in her previous pregnancy. This suggests her previous baby was likely also Rh negative, which is why she didn't develop antibodies. For the current pregnancy, she should receive RhoGAM at 28 weeks and within 72 hours after delivery if the baby is Rh positive, as supported by the most recent study 1. RhoGAM prevents sensitization by neutralizing any fetal Rh positive cells that may enter the mother's circulation, particularly during delivery. This prevention is crucial because if sensitization occurs, in future pregnancies with Rh positive babies, the mother's antibodies could cross the placenta and attack the baby's red blood cells, potentially causing hemolytic disease of the newborn. The standard dose is 300 micrograms intramuscularly, as indicated by previous studies 1. Additional doses may be needed after procedures like amniocentesis or following events that could cause fetal-maternal hemorrhage. Key points to consider include:
- The use of RhD immune globulin has reduced the burden of perinatal morbidity and mortality attributable to RhD alloimmunization 1.
- A postpartum dose of RhIg decreases the rate of postpartum anti-D alloimmunization from between 13% and 17% to 1% to 2% 1.
- The introduction of a postpartum rhesus prevention program reduced fetal mortality from Rh hemolytic disease from 120 per 100,000 live births to 1.5 per 100,000 by 1989 1.
From the FDA Drug Label
CLINICAL PHARMACOLOGY HyperRHO S/D Full Dose is used to prevent isoimmunization in the Rho(D) negative individual exposed to Rho(D) positive blood as a result of a fetomaternal hemorrhage occurring during a delivery of an Rho(D) positive infant, abortion (either spontaneous or induced), or following amniocentesis or abdominal trauma Rh hemolytic disease of the newborn is the result of the active immunization of an Rho(D) negative mother by Rho(D) positive red cells entering the maternal circulation during a previous delivery, abortion, amniocentesis, abdominal trauma, or as a result of red cell transfusion.
The patient is Rh negative and has an antibody screen negative for the antigen, which means she has not developed antibodies against Rh positive blood. This is good because it indicates that she has not been sensitized to Rh positive blood, and the risk of Rh hemolytic disease of the newborn is low. However, since the patient did not receive Rho(D) immune globulin in her last pregnancy, there is a risk of sensitization if she was exposed to Rh positive blood during delivery or any other event that may have caused fetomaternal hemorrhage 2.
From the Research
Rh Negative and Antibody Screen Negative
- The patient is Rh negative and has an antibody screen negative for antigen, which means she has not developed antibodies against the RhD antigen 3, 4.
- This is a good sign, as it indicates that she has not been sensitized to the RhD antigen and is not at risk of developing hemolytic disease of the fetus and newborn (HDFN) in a future pregnancy 4.
Prevention of RhD Alloimmunization
- To prevent RhD alloimmunization, Rh immune globulin (RhIG) is administered to Rh negative women at certain times during pregnancy, such as at 28 weeks of gestation and after delivery of an Rh positive infant 3, 4.
- The administration of RhIG has been shown to be highly effective in preventing maternal Rh alloimmunization, with very low rates of D-antigen sensitization reported in multiple studies of at-risk women 4.
Management of Pregnancy
- The management of pregnancy in Rh negative women with an antibody screen negative for antigen involves routine administration of RhIG and monitoring for any signs of sensitization 3, 4.
- In cases where prevention of RhD alloimmunization is not performed within 72 hours of a potentially sensitizing event, it is still reasonable to administer RhIG within 13 days, and in special cases, administration is still recommended up to a maximum interval of 28 days postpartum 3.