An anti-D immunoglobulin is an antibody to a common human antigen present on red blood cells. Only some people have this antigen, known as D-antigen or Rhesus antigen. Anti-D immunoglobulin is used to prevent medical issues arising from a Rhesus negative woman carrying a fetus that is Rhesus positive. The pregnant woman's immune system may recognize the fetal cells as foreign and attack it. Rhesus negative people who have had Rhesus positive blood transfused can also be given anti-D immunoglobulin.
Human red blood cells carry protein signals on the surface of the cell. One of the most important of these groups is the Rhesus group, and the D-antigen is the most important antigen of that group. In medicine, people who have the D-antigen and whose cells therefore contain the Rhesus group are known as Rhesus positive.
When a woman who is Rhesus negative becomes pregnant, her fetus can be Rhesus positive or negative because it gets some of its genes from the father. Some of the fetal cells can enter the mother's blood, and this can result in the mother developing anti-D immunoglobulin as part of an overall immune response to those cells. This process is known as sensitization. Sensitization is most likely in a first pregnancy, and the risk reduces with each pregnancy.
The mother's anti-D antibodies can cross the placental barrier and get into the fetal blood system. The antibodies bind to the blood cells and remove them from circulation. This can result in fetal anemia. The consequences of fetal anemia can include fetal heart failure, swelling, and death. A baby who is born with anemia can also have jaundice, which if left untreated, can cause brain damage.
The anti-D immunoglobulin is given to Rhesus negative mothers as a preventative measure in the third trimester or in cases where fetal cells are most likely to have crossed into maternal circulation. These cases include women who have had abdominal trauma or invasive procedures, such as amniocentesis. Sometimes, there is no known reason why the fetal cells have crossed over into maternal circulation. The treatment can also be given after delivery.
Anti-D immunoglobulin is also used after miscarriages or abortions. Rhesus negative people who have had a Rhesus positive blood transfusion also need anti-D treatment. Medical anti-D immunoglobulin is purified from blood donations. The plasma component of blood contains the anti-D. The antibody is administered through an injection into muscle or intravenously.