IMMUNE MEDIATED HEMOLYTIC
DISEASE OF THE NEWBORN
Ileana Lopez-Plaza, M.D.
Assistant Medical Director of Transfusion Services
Hemolytic disease of the newborn (HDN) is defined as fetal or neonatal
shortened red cell (RBC) survival that can be caused by inherited RBC membrane defects,
hemoglobinopathies, enzyme deficiencies, acquired intrauterine or perinatal infections, or
red cell antibodies.
Maternal alloimmunization occurs when fetal RBC carrying inherited
paternal RBC antigens which are not present on maternal RBC pass into the maternal
circulation, inducing antibody formation. IgG alloantibodies can then cross the placenta
and coat the fetal RBC that in turn are removed by the macrophage system. First time
pregnancies are rarely involved. However, for subsequent pregnancies in which the fetus
expresses the implicated antigen, severity may increase.
The classic example of maternal alloimmunization is the formation of
anti-D in the Rh negative mother of an Rh positive fetus. Up to 17 % of the Rh negative
pregnant women exposed to Rh positive fetal red cells will develop anti-D. Only 0.1 mL of
red cells are needed to initiate this immune response. However, with the introduction of
Rh immune globulin prophylaxis, the risk of anti-D alloimmunization in this patient
population has decreased to < 0.1 %. Severity of HDN caused by anti-D is variable
ranging from being mild in 50 % of cases to severe in 20 %.
HDN can also be caused by maternal anti-A, anti-B and anti-A,B IgG
isoagglutinins mostly present in type O mothers. Although a type O mother of a type A or B
infant occurs in 15 % of pregnancies the frequency of HDN due to ABO isoagglutinins is
only 1/150 births. Rarely clinically severe, it is manifested mostly in the neonatal
period as a rising indirect bilirubin in the first 36 hours of life with minimal anemia.
The direct antiglobulin (Coombs) test is weakly positive or negative even in the affected
neonates and spherocytes are present in the peripheral blood smear. Most affected neonates
will respond to phototherapy alone. Rh alloimmunization is less likely to occur when ABO
incompatibility between mother and fetus is present.
Other antibodies against red cell antigens can cause HDN. Implicated
antibodies include anti E, anti-c, or anti-K1.
Prenatal Diagnosis and Treatment
The diagnostic evaluation includes maternal prenatal ABO and Rh typing,
and an antibody screen. Depending on the results of the antibody screen, maternal antibody
titers, and paternal and/or fetal RBC phenotyping are performed. If fetal RBC express the
antigen against which maternal alloimmunization has occurred, the pregnancy is then
followed by measuring serial maternal antibody titers and abdominal sonograms.
In response to the shortened RBC survival the fetus compensates by
markedly increasing erythropoiesis. Extramedullary hematopoiesis in the liver can cause
portal hypertension and ascites. If erythropoiesis cannot compensate for the rate of
hemolysis, anemia may occur with consequent high output cardiac failure and anasarca. The
hemolysis results in increased fetal production of indirect bilirubin that crosses the
placenta and undergoes conjugation in the maternal liver, thereby preventing its
accumulation in the fetus. Ultrasonography can provide information on polyhydramnios,
fetal organomegaly and edema. Abnormal ultrasound findings signs are an indication to
measure fetal hemoglobin by percutaneous umbilical blood sampling and/or amniocentesis to
measure bile pigments in the amniotic fluid. The fetus is monitored with serial sonograms,
serial hemoglobin measurements and serial bile pigment measurements. Depending on the
gestational age and fetal lung maturity, intrauterine RBC transfusions are given or early
delivery is performed. Blood used for intrauterine transfusion should be type O negative,
CMV negative, irradiated, Sickledex negative, < 7 days old, crossmatched compatible
with mothers serum, and red cell antigen negative for the offending antibody.
After delivery a direct antihuman globulin test (Coombs), hemoglobin,
and bilirubin level is performed on a cord blood sample. After birth, the maternal liver
is not available for conjugation of the accumulating bilirubin and the neonatal liver is
too immature to handle the bilirubin load, therefore the neonatal unconjugated bilirubin
levels starts to rise. Accumulation of the unconjugated bilirubin puts the neonate at risk
of developing kernicterus with the accompanying neurological sequelae. The rate at which
the indirect bilirubin levels increase dictates what kind of intervention to follow, with
the alternatives including observation, phototherapy, or red cell exchange transfusion.
Exchange transfusion serves several purposes including: reducing the levels of indirect
bilirubin, removing circulating maternal antibodies and antibody coated neonatal RBC and
correcting the anemia.
Gestational alloimmunization with anti-D in Rh negative mothers can be
prevented by the use of RhIg. The risk of alloimmunization has decreased from 17 % to 0.1%
with RhIg prophylaxis. The immunosuppresive effect is believed to result from an
interference with antigen recognition during the induction phase of the primary
immunization. RhIg is a formulation prepared from the plasma of humans sensitized with
anti-D. Its preparation and processing makes it a viral free blood derivative, similar to
albumin. Currently it is available as an intramuscular or intravenous preparation. One
vial contains 300 ug of anti-D which will protect against 30 mL of Rh positive whole blood
or 15 mL of Rh positive RBC. It is recommended that RhIg be given at 28 weeks gestation
and within 72 hours of delivery of an Rh positive neonate. It is known that the majority
of the alloimmunization occurs after 28 weeks of gestation although the expression of the
Rh antigen in the fetus can be expressed as early as the 4th week of gestation. The amount
of fetomaternal hemorrhage (FMH, circulating fetal blood in the mother) is estimated after
delivery in order to provide an adequate RhIg dose. An initial screening test, the rosette
test, will detect a FMH > than 10 mL. If positive, a quantitative test, the
Kleihauer-Betke acid elution test is performed. The amount of RhIg to be given is
calculated based on the quantity of fetal RBC in the maternal blood. It is estimated that
0.3% of FMH are greater than 10 mL. RhIg is also recommended for any obstetrical
intervention or maternal abdominal trauma in the mother which could potentially cause FMH
(i.e. abortion, amniocentesis, chorionic villi sampling, cordocentesis).
Copies of the Transfusion Medicine Update can be obtained by contacting
Deborah Small at (412)