What are the implications of an Rh(Rhesus) negative mother during pregnancy?

From the Guidelines

Rh negative mothers require special attention during pregnancy due to potential blood incompatibility issues, and to prevent sensitization, they should receive Rh immunoglobulin injections at 28 weeks of pregnancy and again within 72 hours after delivery if the baby is Rh positive. If an Rh negative woman carries an Rh positive baby, her immune system may develop antibodies against the baby's blood cells if fetal blood enters her circulation, typically during delivery or pregnancy complications 1. This sensitization usually doesn't affect the current pregnancy but can cause hemolytic disease in future Rh positive pregnancies.

The use of RhD immune globulin (RhIg) has reduced the burden of perinatal morbidity and mortality attributable to RhD alloimmunization 1. Among RhD-negative patients, 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.

Some key points to consider in the management of Rh negative mothers include:

• Blood typing is done early in pregnancy to identify Rh status, and antibody screening monitors for any existing sensitization 1.
• Additional doses of RhIg may be needed after procedures like amniocentesis or if vaginal bleeding occurs 1.
• 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, but a 300 mg RhIg dose may be used when the lower dose is unavailable 1.
• Administration of a lower dose may decrease the concern for resource over-utilization with RhIg administration, and if a typically used brand of RhIg is not available, an equivalent RhIg product may be substituted if available 1.

From the FDA Drug Label

HyperRHO S/D Full Dose is recommended for the prevention of Rh hemolytic disease of the newborn by its administration to the Rho(D) negative mother within 72 hours after birth of an Rho(D) positive infant,(12) providing the following criteria are met: 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. (7,8)

An Rh negative mother in pregnancy is at risk of developing Rh isoimmunization if she is exposed to Rh positive blood from her fetus. This can occur during pregnancy, childbirth, abortion, or certain medical procedures like amniocentesis. To prevent this, Rh immune globulin is administered to the mother within 72 hours of delivery of an Rh positive infant. The goal is to suppress the immune response and prevent the formation of anti-Rh antibodies that can attack the fetus's red blood cells in future pregnancies 2.

• Key points:
  • Rh negative mother: at risk of Rh isoimmunization
  • Rh isoimmunization: can occur during pregnancy, childbirth, or certain medical procedures
  • Prevention: administration of Rh immune globulin within 72 hours of delivery of an Rh positive infant
  • Goal: suppress immune response and prevent formation of anti-Rh antibodies 2

From the Research

Rh Negative Mother in Pregnancy

• An Rh-negative mother is at risk of developing Rh isoimmunization when exposed to RhD antigens from her Rh-positive baby through fetal-maternal hemorrhage 3.
• The incidence of Rh isoimmunization and fetal hemolytic disease has decreased substantially since Rh immune globulin was introduced in 1968 3, 4.
• To prevent Rh isoimmunization, anti-D immune globulin is given to Rh-negative mothers at 28 weeks' gestation and within 72 hours of delivery if the baby is Rh-positive 5.
• The dose of anti-D immune globulin may vary depending on the amount of fetal-maternal hemorrhage, with additional doses given if necessary 5, 3.
• It is essential to type and screen all pregnant women for alloantibodies, including Rh factor, at the first prenatal visit and again at 28 weeks 5.

Prevention and Management

• Anti-D immune globulin is ~99% effective in preventing maternal sensitization to RhD when given antenatally and post-partum 4.
• However, it is estimated that ~50% of women worldwide who require this immunoprophylaxis do not receive it, putting hundreds of thousands of fetuses and neonates at risk for Rh disease each year 4.
• Careful follow-up and judicious intervention can result in good outcomes for most pregnancies affected by Rh isoimmunization 3.
• Doppler assessment of middle cerebral artery peak systolic velocity and spectral analysis of amniotic fluid at 450 nm (DeltaOD 450) are useful in the diagnosis and management of fetal anemia 3.

Historical Context

• The discovery of the Rh factor and its role in hemolytic disease of the fetus and newborn has led to significant advances in the prevention and management of Rh isoimmunization 6.
• Routine Rh typing of all prospective recipients of transfusion and giving only Rh-negative blood to those who are Rh-negative can avoid the dangers of Rh sensitization 6.