Rhesus incompatibility Flashcards
(12 cards)
What does rhesus refer to?
Various types of rhesus antigens on the surface of RBCs which can vary between individual and the rhesus antigens are separate to the ABO blood group system.
What is the most relevant antigen within the rhesus blood group system?
Rhesus-D antigen and in pregnancy this is what you are referring to.
What happens to rhesus-D positive women when they fall pregnant?
No additional treatment.
What happens to rhesus-D negative women when they fall pregnant?
If the child is rhesus positive and baby’s blood enters mother’s blood, the baby’s RBCs will display rhesus D antigen and the mother’s immune system will produce antibodies to it and become sensitised.
What is the problem with the sensitisation process?
Usually doesn’t cause problems in the first pregnancy but in other pregnancies, the mother’s anti-rhesus D antibodies can cross the placenta into the fetus. If that fetus is rhesus D positive, the antibodies will attach themselves to fetus RBCs which causes immune system of fetus to attack them, destroying blood cells. This is called haemolytic disease of the newborn.
What is the management?
Preventing sensitisation by giving IM anti-D injections to rhesus D negative women.
How does the anti-D injection work?
Attaches itself to rhesus D antigens on the fetal RBCs, causing them to be destroyed, preventing mother’s immune system from recognising the antigen and creating its’ own antibodies to the antigen.
When are the anti-D injections given routinely?
28 weeks gestation and at birth if baby’s blood group is found to be rhesus-positive.
When additionally could they be given?
Any time where sensitisation could occur such as:
- Antepartum haemorrhage
- Amniocentesis procedures, chorionic villus sampling, fetal blood sampling
- Abdominal trauma
- surgical management of ectopic pregnancy
What time frame is anti-D given in after a sensitisation event?
Given within 72 hours of a sensitisation event. After 20 weeks gestation, the Kleihauer test is performed.
What is the Kleihauer test?
Checks how much fetal blood has passed into the mother’s blood during a sensitisation event. Acid is added to a sample of mother’s blood. Fetal Hb is more resistant to acid so is protected against acidosis which occurs around childbirth, so fetal Hb will persist whilst mother’s Hb is destroyed. The number of cells still containing the Hb (remaining fetal cells) can then be calculated.
- carried out in order to calculate how much anti-D immunoglobulin needs to be given to the mother
When is Kleihauer test done?
After 20 weeks gestation, to see how much fetal blood has passed into the mother’s blood, to determine whether further doses of anti-D are required.
