What does Rh negative status mean for the pregnant individual?

From the Guidelines

Rh negative blood type in a pregnant person means they lack the Rhesus (Rh) factor on their red blood cells, which can lead to the production of anti-D antibodies if exposed to Rh-positive blood, potentially causing hemolytic disease of the newborn in subsequent pregnancies. This becomes medically significant when an Rh-negative mother is pregnant with an Rh-positive baby. If the mother's blood mixes with the baby's blood during pregnancy or delivery, the mother's immune system may recognize the baby's Rh factor as foreign and produce antibodies against it. While this typically doesn't affect a first pregnancy, these antibodies can cross the placenta in subsequent pregnancies with Rh-positive babies, attacking the baby's red blood cells and causing hemolytic disease of the newborn.

Key Considerations

• The use of RhD immune globulin (RhIg) has reduced the burden of perinatal morbidity and mortality attributable to RhD alloimmunization, as noted in a 2024 study published in the American Journal of Obstetrics and Gynecology 1.
• A postpartum dose of RhIg decreases the rate of postpartum anti-D alloimmunization from between 13% and 17% to 1% to 2%, and an additional dose in the mid-trimester reduces the antepartum rate of alloimmunization from 1.8% to between 0.1% and 0.2% 1.
• To prevent RhD alloimmunization, Rh-negative pregnant women should receive RhoGAM (Rh immunoglobulin) injections at around 28 weeks of pregnancy and within 72 hours after delivery if the baby is Rh-positive, with a standard dose of 300 micrograms intramuscularly, as recommended by a 2024 statement from the Society for Maternal-Fetal Medicine 2.

Administration of RhIg

• When RhIg administration is indicated, a 50 mg dose within 72 hours of the spontaneous or induced abortion is adequate to cover the volume of potential feto-maternal hemorrhage in the first trimester, although a 300 mg RhIg dose may be used when the lower dose is unavailable 2.
• In cases where the supply of RhIg is limited, postpartum patients and antenatal patients at later gestational ages should be prioritized for the available doses, and an equivalent RhIg product may be substituted if available 2.

From the FDA Drug Label

The mother must be Rho(D) negative and must not already be sensitized to the Rho(D) factor. 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. 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

Being Rh negative for a pregnant person means that they have a higher risk of developing Rh isoimmunization if they are exposed to Rh positive blood, which can occur during pregnancy, childbirth, or abortion. This can lead to the production of anti-Rh antibodies, which can cause Rh hemolytic disease of the newborn in future pregnancies. To prevent this, Rh immune globulin is administered to Rh negative mothers within 72 hours of delivery of an Rh positive infant 3, 4. Key points include:

• Rh negative mothers are at risk of isoimmunization if exposed to Rh positive blood
• Rh immune globulin is used to prevent isoimmunization in Rh negative individuals
• Administration of Rh immune globulin within 72 hours of delivery can reduce the incidence of Rh isoimmunization 3, 4

From the Research

Rh Negative Pregnancy

Being Rh negative during pregnancy means that the pregnant person has Rh negative blood type, and their baby may have Rh positive blood type if the father is Rh positive. This can lead to complications if the baby's Rh positive blood cells enter the mother's bloodstream, causing her immune system to react and produce antibodies against the Rh positive cells.

Risks and Complications

• The main risk is the development of Rh isoimmunization, which can occur when the mother's immune system is exposed to the baby's Rh positive blood cells 5.
• This can lead to the production of antibodies that can cross the placenta and attack the baby's red blood cells, causing hemolytic disease of the fetus and newborn (HDFN) 5, 6.
• The risk of Rh isoimmunization is higher in women who undergo invasive prenatal testing, such as chorionic villus sampling (CVS) or amniocentesis, without receiving Rh immune globulin (RhIg) 7.

Prevention and Management

• RhIg is administered to Rh negative pregnant women to prevent Rh isoimmunization 8, 5.
• The dose and timing of RhIg administration depend on the gestational age and the presence of any potentially sensitizing events, such as abortion, ectopic pregnancy, or invasive prenatal testing 8.
• Cell-free DNA (cfDNA) testing can be used to determine the fetal RhD status and prioritize RhIg administration in cases of shortage 6.
• Close monitoring and follow-up are essential for women who develop Rh isoimmunization to ensure good outcomes for the pregnancy 5.