HDN is not an allergic reaction, but an immune response to a foreign antigen. Unlike allergy which is a Type I Hypersensitivity reaction mediated by IgE antibodies, HDN is a Type II reaction of the immune system precipitated by IgG and IgM antibodies.

Hemolytic disease of the newborn, otherwise, Erythroblastosis fetalis is a condition that develops due to certain blood incompatibilities between the fetus and the mother. Primarily, it is due to an incompatibility of the Rh group, but may also be caused by incompatibility of ABO blood group. Uncommon causes are antigen-antibody reaction of the Kell, Kidd, Duffy, and MNS blood group.

Sensitization

HDN occur when fetal red blood cells possess antigens that the mother does not. The red blood cells can pass through the placenta and into the maternal circulation secondary to trauma, miscarriage, placental rupture during gestation, or medical procedures (e.g. amniocentesis, chorionic villi sampling) that cause disruption of the uterine wall.

Sensitization takes place on the first pregnancy, as the body initially encounters the unfamiliar antigens from fetal red blood cells. The immune system is sensitized and develops IgM antibodies against that antigen. IgM cannot cross the placental barrier, however, on the following pregnancy of the same case, the body rapidly produces IgG antibodies that are able to cross the placenta and wreak havoc in the fetal bloodstream.

Erythroblastosis fetalis

In Rh factor incompatibility, a hemolytic reaction occurs only when the mother is Rh negative and the fetus is Rh positive. During sensitization, the mother has developed antibodies against the antigens that are present on the surface of fetal red blood cells. On the following pregnancy, IgG antibodies from the mother travel into fetal circulation and binds with the cell-bound antigen. The result of the antigen-antibody binding is the activation of the complement cascade and destruction of the red blood cells.

Rh incompatibility results into a more severe reaction that ABO incompatibility.  That is because ABO-incompatible RBCs are immediately destroyed in the mother’s circulation.

Clinical Presentation

RBC destruction or hemolysis causes elevated bilirubin levels that are evident as jaundice during the first 24 hours after delivery. Eventually, hemolysis (RBC destruction) leads to anemia. Prenatal complications include fetal hydrops, and enlargement of the liver and spleen. During delivery, there will be an increased of respiratory distress, kernicterus, low blood sugar levels, and pulmonary hypertension. The fetus may either be stillborn or die shortly after delivery.

What your Doctor can do for you

Other disorders must be ruled out to establish the diagnosis of HDN. A Coomb’s test is used to detect HDN. It may either be direct—testing for maternal antibodies that are bound to fetal RBCS in fetal circulation; or indirect—testing for the development of antibodies in the maternal circulation.

There will be a number of preparations and monitoring needed to be done during gestation and prior to delivery to protect the health of the mother and fetus.

An Indirect Coomb’s test will determine if the mother has already been sensitized. If not, RhoGAM or Rh Immune globulin will be administered intramuscularly to the mother on the 28th week of pregnancy and within 72 hours after delivery to eradicate fetal RBCs that is transmitted to the mother. Other treatment options include intrauterine transfusion for the fetus, or plasma exchange for the mother.

Consult your Doctor about the course of therapy as this may vary for each individual. The rest of the treatment shall be discussed by the physician.

What you can do

A pregnant woman should always adhere to the prescribed prenatal visits to her obstetrician. Pregnancy entails a number of precautions due to the vulnerability of a woman and her child’s state. HDN is a life-threatening condition but can be managed with due assistance and compliance to the doctor’s advice. Seek medical attention and do not simply rely on readings for you to be sure of the wellness your condition.