Rhesus Incompatibility Flashcards
Rhesus D-positive vs rhesus-D negative women?
Women that are rhesus-D positive do not need any additional treatment during pregnancy.
When a woman that is rhesus-D negative becomes pregnant, we have to consider the possibility that her child will be rhesus positive. It is likely at some point in the pregnancy (i.e. childbirth) that the blood from the baby will find a way into the mother’s bloodstream. The mother’s immune system will recognise this rhesus-D antigen as foreign, and produce antibodies to the rhesus-D antigen. The mother has then become sensitised to rhesus-D antigens.
Usually, this sensitisation process does not cause problems during the first pregnancy. During subsequent pregnancies, the mother’s anti-rhesus-D antibodies can cross the placenta into the fetus. If that fetus is rhesus-D positive, these antibodies attach themselves to the red blood cells of the fetus and causes the immune system of the fetus to attack them, causing the destruction of the red blood cells (haemolysis). The red blood cell destruction caused by antibodies from the mother is called haemolytic disease of the newborn.
Management of rhesus-D negative mothers?
Prevention of sensitisation is the mainstay of management. This involves giving intramuscular anti-D injections to rhesus-D negative women. There is no way to reverse the sensitisation process once it has occurred, which is why prophylaxis is so essential.
The anti-D medication works by attaching itself to the rhesus-D antigens on the fetal red blood cells in the mothers circulation, causing them to be destroyed. This prevents the mother’s immune system recognising the antigen and creating its own antibodies to the antigen.
Anti-D injections are given routinely on two occasions:
28 weeks gestation
Birth (if the baby’s blood group is found to be rhesus-positive)
Anti-D injections should also be given at any time where sensitisation may occur, such as:
Antepartum haemorrhage
Amniocentesis procedures
Abdominal trauma
Anti-D is given within 72 hours of a sensitisation event. After 20 weeks gestation, the Kleinhauer test is performed to see how much fetal blood has passed into the mother’s blood, to determine whether further doses of anti-D are required.
What is Kleihauer test?
The Kleihauer test checks how much fetal blood has passed into the mother’s blood during a sensitisation event. This test is used after any sensitising event past 20 weeks gestation, to assess whether further doses of anti-D is required.
