05/07/2026
BLOOD GROUP INCOMPATIBILITY
Rh disease (also called isoimmunization or alloimmunization) is an immune reaction that occurs when a person develops antibodies against red blood cell antigens from another individual. In pregnancy, this most commonly happens when an Rh-negative mother carries an Rh-positive fetus.
Small amounts of fetal blood enter the maternal circulation (during delivery, miscarriage, trauma, invasive procedures, or bleeding in pregnancy).
The Rh-negative mother's immune system recognizes the fetal Rh(D) antigen as foreign.
She produces anti-D IgG antibodies (sensitization).
In a subsequent Rh-positive pregnancy, these IgG antibodies cross the placenta and destroy fetal red blood cells.
This causes fetal anemia and hemolysis leading to spontaneous miscarriages.
RISK FACTORS
▪️Rh-negative mother carrying an Rh-positive fetus
▪️Previous pregnancy with an Rh-positive baby
▪️Previous miscarriage, abortion, ectopic pregnancy, or blood transfusion
▪️Bleeding during pregnancy or abdominal trauma
TYPES
1. Rh incompatibility
Mother is Rh-negative and the baby is Rh-positive.
The mother may develop antibodies against the Rh(D) antigen if exposed to the baby's blood.
These antibodies can affect the current or future Rh-positive pregnancies.
Prevention is with Rho(D) immune globulin.
2. ABO incompatibility
Most commonly occurs when the mother has blood group O and the baby has blood group A, B, or AB.
It is usually milder than Rh incompatibility.
The newborn may develop jaundice or mild anemia, which is often treated with phototherapy if needed.
CAUSES
Rh(D) incompatibility (most common)
Other blood group incompatibilities (e.g., Kell, Duffy, Kidd antibodiesu cases)
In the newborn:
Jaundice
Anemia
Hyperbilirubinemia
Kernicterus (if severe untreated)
DIAGNOSIS
Maternal blood grouping and Rh typing
Indirect Coombs test (maternal antibody screen)
Antibody titers
Middle cerebral artery (MCA) Doppler to detect fetal anemia
Direct Coombs test on neonatal blood after birth
PREVENTION
The most effective prevention is administration of Rho(D) immune globulin to Rh-negative, unsensitized mothers:
At 28 weeks of gestation
Within 72 hours after delivery of an Rh-positive baby
After miscarriage, ectopic pregnancy, abortion, antepartum hemorrhage, abdominal trauma, or invasive procedures (e.g., amniocentesis)
MANAGEMENT
Monitor maternal antibody titers.
Serial fetal surveillance with MCA Doppler.
Intrauterine blood transfusion if severe fetal anemia develops.
Early delivery when appropriate.
After birth: phototherapy, exchange transfusion, or packed red blood cell transfusion depending on severity.
KEY POINT:
Isoimmunization occurs when maternal antibodies attack fetal red blood cells, leading to Hemolytic disease of the fetus and newborn. Prevention with anti-D immunoglobulin has dramatically reduced Rh isoimmunization.
