|MadSci Network: Immunology|
Amina MOUJTAHID, Good question! Ok, first let's review. As you know, a woman who is Rh negative means that she does not have what is called the "D antigen" on her red blood cells. Some people call the "D antigen" the Rh antigen. An antigen is a molecule on the surface of the red blood cell that can cause antibodies to form. When you hear someone say AB pos or O neg, the positive means that they have the Rh antigen and the negative means they don't have the Rh antigen. Ok, so far? Now, if you are Rh negative, you not only don't have the antigen, but you MIGHT make antibodies to Rh positive blood. Normally, though, women with Rh negative blood don't get exposed to Rh positive blood, except when they are pregnant! If her child is Rh positive and she is exposed to her baby's blood when the baby is delivered, then she will make new antibodies to Rh positive antigens. Not a problem for her first baby! But what about a second baby?? Well, if the baby is Rh negative, then her new antibodies can't hurt a thing, because the baby doesn't have the Rh antigen! But, if her baby is Rh positive, then watch out! Because then her new Rh antibodies can attack the red blood cells of the baby, causing a condition called erythroblastosis fetalis. Not good for the second Rh positive baby. Ok, enough review! What about RhoGAM? If you look again, you will see that this whole scene occurs because the Rh negative mother develops antibodies to Rh antigens. It's the new antibodies that's the problem. So, what RhoGAM does is prevent the antibodies from forming in the first place! And here's how it does it. Immediately before or after each delivery, the obstetrician will administer RhoGAM (that answers one of your questions!). RhoGAM is actually antibodies itself! The RhoGAM antibodies then attach to the Rh positive red blood cells of the baby(if it has any Rh antigen). This covers the Rh antigen, so that the mother's immune system cannot make antibodies to it! So, since the mother doesn't make antibodies, she can't hurt the second baby. Of course, RhoGAM has to be given at each birth so that she doesn't hurt the next child. For a reference, see the following: Anatomy & Physiology, 2nd edition, Seeley, Stephens, Tate, Moseby-Year Book, Inc., ISBN 0-8016-4832-7, p.602-603
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