What is the significance of Rhesus (Rh) factor in medical diagnosis?

From the Guidelines

Rh-negative pregnant women should receive RhoGAM (Rh immunoglobulin) injections at 28 weeks of pregnancy and within 72 hours after giving birth to an Rh-positive baby to prevent Rhesus incompatibility and hemolytic disease of the newborn in subsequent pregnancies. Rhesus refers to the Rhesus (Rh) factor, which is a protein found on the surface of red blood cells. People who have this protein are Rh-positive, while those without it are Rh-negative. The most significant concern with Rhesus status arises during pregnancy when an Rh-negative mother carries an Rh-positive baby, potentially leading to Rhesus incompatibility. If an Rh-negative woman becomes pregnant with an Rh-positive fetus, her immune system may develop antibodies against the baby's blood cells, causing hemolytic disease of the newborn in subsequent pregnancies.

According to a study published in the American Journal of Obstetrics and Gynecology 1, the use of RhD immune globulin (RhIg) has reduced the burden of perinatal morbidity and mortality attributable to RhD alloimmunization. The study found that 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%.

Key points to consider:

• Rhesus factor testing is a routine part of prenatal care and blood typing, ensuring appropriate management of potential incompatibility issues.
• The standard dose of RhoGAM is 300 micrograms intramuscularly.
• RhIg administration reduces the risk of RhD alloimmunization with spontaneous and induced abortion, although the specific point estimate has not been determined 1.
• A study published in the Annals of Emergency Medicine 1 found that 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.

Overall, the administration of RhIg to Rh-negative pregnant women is a crucial step in preventing Rhesus incompatibility and reducing the risk of hemolytic disease of the newborn in subsequent pregnancies.

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 term rhesus refers to the Rho(D) blood type system. The drug label discusses the use of Rh immune globulin (IM) to prevent isoimmunization in Rho(D) negative individuals exposed to Rho(D) positive blood.

• The mechanism of action of HyperRHO S/D Full Dose is not fully understood, but it acts by suppressing the immune response of Rho(D) negative individuals to Rho(D) positive red blood cells 2.
• The administration of Rho(D) Immune Globulin (Human) can reduce the incidence of Rh isoimmunization in Rho(D) negative mothers carrying Rho(D) positive infants.

From the Research

Rhesus Alloimmunization Prevention

• The prevention of Rh alloimmunization is crucial in Rh-negative women, and guidelines have been established to optimize this process 3.
• Anti-D immune globulin (Anti-D Ig) is administered to Rh-negative women to prevent Rh alloimmunization, with specific dosages and timing recommended based on the situation 3, 4.

Dosage and Administration

• The recommended dose of Anti-D Ig is 300 micrograms IM or IV within 72 hours of delivery to a postpartum nonsensitized Rh-negative woman delivering an Rh-positive infant 3.
• Additional Anti-D Ig may be required for fetomaternal hemorrhage (FMH) greater than 15 mL of fetal red blood cells 3.
• If Anti-D is not given within 72 hours of delivery or other potentially sensitizing event, it should be given as soon as the need is recognized, for up to 28 days after delivery or other potentially sensitizing event 3.

Screening and Testing

• All pregnant women (D-negative or D-positive) should be typed and screened for alloantibodies with an indirect antiglobulin test at the first prenatal visit and again at 28 weeks 3.
• The erythrocyte rosette test can be used to screen for excessive fetomaternal hemorrhage in Rh-negative women, with a higher sensitivity compared to the Du test 5.
• Quantitative testing for FMH may be considered following events potentially associated with placental trauma and disruption of the fetomaternal interface 3, 6.

Special Considerations

• A woman with "weak D" (also known as Du-positive) should not receive Anti-D 3.
• Verbal or written informed consent must be obtained prior to administration of the blood product Rh immune globulin 3.
• Massive fetomaternal hemorrhage can occur without any antecedent risk factors, and prompt administration of adequate amounts of Rh immune globulin can prevent sensitization 4, 7.