Red blood cell isoimmunization Flashcards
What happens in red blood cell isoimmunisation?
It is when the mother mounts an immune response against antigens on foetal red cells that enter her circulation. The resulting antibodies then cross the placenta and cause foetal red blood cell destruction.
What is sensitisation to Rhesus D?
Small amounts of foetal blood cross the placenta and enter the maternal circulation during uncomplicated pregnancies and particularly at sensitising events, such as delivery. If a Rhesus negative mother (dd) has a Rhesus positive child (Dd), the mother will mount an immune response (sensitisation), creating anti-D antibodies. Immunity is permanent.
How do you prevent production of maternal anti-D?
My administration of exogenous anti-D to the mother. This ‘mops up’ foetal red cells that have crossed the placenta, by binding their antigens, thereby preventing recognition by the mother’s immune system.
What are potentially sensitising events for foetal blood to pass into the maternal circulation?
Termination of a pregnancy or evacuation of retained foetal products after miscarriage. Ectopic pregnancy. Vaginal bleeding >12 weeks External cephalic version Amniocentesis/chorionic villus sampling Intrauterine death Delivery
What happens when a sensitised mother has a Rhesus D positive baby?
When the mother’s immune system is exposed again to the antigen, large numbers of antibodies are rapidly created. They can cross the placenta and bind to foetal RBCs, which are then destroyed in the foetal reticuloendothelial system. This can cause haemolytic anaemia and ultimately death –> Rhesus haemolytic disease of the newborn.
When is anti-D given to women?
Rhesus negative women carrying a baby who is Rhesus positive or whose status is unknown will receive anti-D at 28 weeks.
They are also given anti-D within 72 hours of any sensitising event.
The neonates blood type is checked after delivery and if Rhesus positive, the mother will have more anti-D within 72 hours of delivery.
A Kleihauer test, to assess the number of foetal cells in the maternal circulation, is also performed within 2 hours of birth to detect occasional larger foetal haemorrhages that require larger doses of anti-D to ‘mop up’.
What are the varying degrees of manifestation of Rhesus disease?
As antibody levels rise in the mother, they will cross the placenta and cause haemolysis.
Mild = neonatal jaundice.
Significant = neonatal anaemia.
Severe = neonatal anaemia - cardiac failure, ascites and oedema (hydrops) and foetal death.
How is the severity of foetal anaemia assessed?
Doppler ultrasound of the peak velocity in systole of the foetal middle cerebral artery has a high sensitivity for significant anaemia.
How is foetal blood sampling performed for anaemia?
Under US guidance, using a needle in the umbilical vein at the cord insertion in the placenta, or in the intrahepatic vein.
What is the treatment for foetal anaemia?
In utero transfusion of Rhesus negative blood. This is repeated at longer intervals as more of the foetal blood is donor Rhesus negative and therefore not subjected to haemolysis.
