Re: Why do we give ANTI SERA D to a mother in ERYTHROBLASTOSIS FETALIS?

M.,

Erythroblastosis fetalis is a disease of the unborn child. It is 
characterized by marked anemia, heart failure, generalized body swelling 
and a greatly accelerated production of fetal red blood cells. It is 
caused by maternal antibodies crossing the placenta into the fetal 
circulation and destroying the fetus' red blood cells. Erythroblasts are 
the immature red blood cells that are being produced to keep up with their 
destriction, hence the term erythroblastosis.

In general, red blood cells have genetically determined proteins on their 
cell surface. These proteins act as antigens. The comon blood types are 
type A, B and AB. Type A has A proteins, B has B proteins, AB has both and 
if there are none then that is called type O. If you get a transfusion of 
blood that is different from your type your body will make antibodies 
against it and destroy those foreign cells. This can cause a lot of 
problems and can even be fatal.

There are other red cell surface antigens in addition to A & B. The 
Rhesus, or Rh, antigens are the major cause of erythroblastosis fetalis. 
They are a group of antigens, the most dominant of which is called D. If 
you have D you are Rh positive, if no D then Rh negative.

In general, the mothers blood and the fetus' blood are separate. But, 
sometimes there is leakage of fetal blood into the maternal circulation. 
If the mother is Rh(-) and the fetus Rh(+) and some of the fetal blood 
leaks into the mother, she will make antibodies against that blood and 
destroy it. These antibodies cross the placenta into the fetal blood 
stream and begin to destroy all the fetal blood. The fetus becomes very 
anemic and tries to make more blood to keep up. The consequences of this 
is a a swollen, edmatous fetus with jaundice and enlarged liver in heart 
failure. The fetus usually dies. The first pregnancy is usually protected 
because it take some time for the mother to become sensitized and the most 
frequent time for leakage is during delivery.

The mother can be tested to see if she has antibodies against Rh(+) blood. 
If she doesn't then she is given an injection of anti D antibodies to 
destroy any fetal blood that may leak into her circulation. Otherwise, 
once she becomes sensitized to Rh(+) blood it is too late and subsequent 
pregnancies are at risk. Anti D is also called RhoGam and is given to all 
nonsensitized pregnant women if they have a miscarriage, abortion, at 28 
weeks pregnancy and within 48 hours of delivery. 

The Rh status of the fetus is determined by the Rh status of the mother 
and father.To be Rh(+) you need only on of the pair of chromosomes to have 
the gene for D. If both pairs have the gene then you are DD, if only one 
has the gene you are Dd. The Rh(-) mother has to be dd. That means she can 
contribute only a d to the fetus. The father, if he is DD can only 
contribute a D, therfore the fetus will be Dd and Rh(+). If the father is 
Dd then there is a 50% chance of a rh(+) fetus and 50% chance to be Rh(-).

The discovery of the ABO and Rh blood types was a great scientific 
accomplishment and has made possible routine blood transfusion and by 
extension organ transplants. It was one of the greates discoveries in all 
medicine.