RHESUS ISOIMMUNIZATION

Rh blood group incompatibility arises when an Rh-negative woman conceives an Rh-positive fetus. RBCs from the fetus can enter the woman’s circulation during pregnancy or, more commonly, during birth. These “foreign” RBCs stimulate the production of maternal anti-bodies against the Rh factor. Spontaneous or induced abortions of an Rh-positive fetus can also result in isoimmunization. In subsequent pregnancies, transplacental transmission of the maternal anti-Rh antibody leads to hemolytic anemia in the fetus or neonate. The resulting disease, called erythroblastosis fetalis, may be fatal. Unless a woman was previously sensitized by transfusion, a first pregnancy rarely leads to erythroblastosis fetalis. Isoimmunization does not have signs or symptoms during pregnancy, although hydrops fetalis and fetal demise may occur in severe cases. In less severe cases, bilirubin levels in the newborncan increase dramatically because of the hemolytic anemia. This can lead to kernicterus, characterized by decreased tone, poor feeding, apnea, seizures, and death. Survivors of kernicterus can be left with mental retardation, choreoathetosis, and hearing loss.

High maternal anti-Rh antibody titers, checked in Rh-negative women at the first prenatal visit and at week 26, suggest sensitization of the mother. Amniocentesis showing high bilirubin levels in theamniotic fluid suggests more severe disease and potential for fetal death.

If bilirubin levels are elevated, intrauterine transfusions to the fetus can be performed at 2-week intervals. Delivery should be minimally traumatic, and the placenta should not be manually removed.

Inthe neonate, hyperbilirubinemia may necessitate phototherapy or an exchange transfusion.
At the first prenatal checkup, all patients should be screened for Rh type. If the patient is Rhnegative, maternal Rh antibody titers should be checked early in the pregnancy and repeated at the twenty-sixth week of gestation. A previously unsensitized mother will not normally produce anti-Rh antibody until after delivery, when mixing of the maternal and fetal blood occurs. Rh isoimmunization can be prevented by injecting the mother with anti-Rh immunoglobulin (RhoGAM) at 28 weeks and within 3 days of delivery. Immunoglobulin C binds the fetal Rh factor and prevents the mother from developing anti-Rh antibodies but is too large to pass though the placenta to the Rh-positive fetus. RhoGAM should be given at the termination of each pregnancy, whether a delivery, ectopic pregnancy, or abortion, as well as any other time when feto-maternal hemorrhage may occur (e.g., amniocentesis or trauma).