Rhesus factor is the name of several proteins found on the erythrocyte membrane. The most important of these is the D-antigen, which determines whether our blood group is Rh (+) or Rh (-).
BLOOD TYPES AND PREGNANCY
One form of blood type incompatibility between the mother and the fetus is Rh incompatibility. It occurs when the Rh negative mother is pregnant with an Rh-positive fetus. To determine the probability of the fetus being Rh (+), the father’s blood gets tested. If he is Rh (-), there is no risk of immunological conflict between the mother and the fetus, as the fetus will also have Rh (-) blood.
During pregnancy, the mother’s blood doesn’t come into contact with the blood of the fetus. When this occurs (at birth, abortion, etc.), the mother’s body makes antibodies against the Rh antigen on the baby’s erythrocytes.
This isn’t dangerous to the baby if this is the first pregnancy. In subsequent pregnancies with an Rh (+) fetus, these antibodies can cross the placenta and start attacking the erythrocytes of the fetus. This can easily be prevented by injecting a drug called anti-D gamma globulin at 28 weeks. After birth, the baby’s blood has to be tested. If it’s Rh(+), the mother gets another dose of anti-D gammaglobulin.
It is important that prophylaxis with anti-D gammaglobulin is done even after an abortion, as it also leads to the formation of antibodies.
The second case of blood type incompatibility between mother and fetus is when the mother’s blood type is 0 and the fetus’s blood type is A, B or AB. Natural anti-A or anti-B antibodies from the mother’s blood may pass through the placenta only when their molecule is smaller (IgG class). Although rare, when it happens the baby is born with transient anemia and jaundice that are treatable.
HEMOLYTIC DISEASE OF THE NEWBORN
It develops when prophylaxis with anti-D gammaglobulin is not performed. In milder cases, babies are born with jaundice and hepatomegaly (enlarged liver). Serious forms are life-threatening, resulting in premature birth, anemia, oedema, and intense jaundice.
THE RAREST BLOOD TYPE
Those people don’t have any antigens of the Rh system on their red blood cells. This makes their blood compatible with any Rh phenotype. Only 44 people in the world are known to have the “golden” blood.