What is antibody M? A friend of mine is pregnant, and the doctor used this term and is testing her monthly. Does it have anything to do with Rh factor problems?

--Mary

On all red blood cells are substances called antigens -- more than 400 have been identified, including the Rh factor. If a woman does not have a certain antigen (for example, if she is Rh-negative), then she may produce antibodies when exposed to that antigen through blood transfusion or from pregnancy. During pregnancy there may be some transfer of fetal blood into the mother's circulation. If the father has a certain antigen that the mother doesn't, and the baby inherits the gene to produce that antigen from dad, then the presence of the fetal antigen in the mother's blood may cause the mom to become "sensitized," meaning her body will see the fetal antigen as a foreign substance, and will produce antibodies against it. These antibodies can then cross the placenta, attacking the red blood cells of the fetus and leading to anemia. In some cases, such as Rh factor incompatibility, this can be severe, producing such profound anemia that the baby goes into heart failure.

M is one of these red blood cell antigens. M may cause problems in pregnancy, so doctors generally monitor it by testing the mother's blood antibody levels. If the antibody level is low and does not increase, then the baby should have no problems. In general, if the antibody level rises to more than 1:16, further evaluation with amniocentesis or direct sampling of fetal blood is called for. If fetal anemia is diagnosed, the baby is either given a transfusion or delivered, depending on how far along the pregnancy is. These complicated pregnancies are managed by specialists in maternal-fetal medicine (otherwise known as perinatologists).

This is a complicated subject, and your friend should sit down with her obstetrician and get all the facts as they pertain to her. If she has an increase in antibody levels, or if she would just like a second opinion, then she should see a perinatologist.