Red blood cell isoimmunisation Flashcards
What is red blood cell isoimmunisation?
It occurs when the mother amounts an immune response against antigens on fetal red cells that enter her circulation. The resulting antibodies then cross the placenta and cause fetal red blood cell destruction
What are the alleles needed to be rhesus positive, how does rhesus work?
D is dominant so anything other than dd are rhesus positive, if the mother is negative then anything other than rhesus negative there will be a reaction which anti-D antibodies
What happens if an affected mother has a second pregnancy?
Immunity is permanent, if the mother is exposed again large numbers of antibodies are rapidly created, they cross the placenta and bind to fetal RBCs, which are then destroyed by the fetal reticuloendothelial system, causing haemolytic anaemia
What are the effects of haemolytic anaemia caused by rhesus sensitivity? (a.k.a rheusus haemolytic disease)
It can lead to death
What are some potentially rhesus sensitising events?
Termination of pregnancy Ectopic pregnancy Vaginal bleeding <12 weeks, or if heavy External cephalic version Invasive uterine procedure (CVS/amniocentesis) Intrauterine death Delivery
How can rhesus sensitivity be avoided?
Production of maternal anti-can be prevented by the administration of exogenous anti-D to the mother.
How does an anti-D injection work?
It mops up fetal red blood cells that have crossed the placenta, by binding to their antigens, hereby preventing recognition by the mother’s immune system.
Who is anti-D given to?
All rhesus negative mothers at 28 weeks, even if the father is rhesus negative also, due to non-paternity, which must be handled with care.
Can anti-D be given after sensitisation?
It can be given within 72hrs of any sensitising event, although some benefit is gained within 10 days.
What does a Kleihauer test measure?
It assesses the number of fetal cells in the maternal circulation.
What ethnicity is rhesus negativity most common?
15% of caucasian women are, but fewer African or asian women are rhesus negative
How does mild rhesus disease present?
It can lead to neonatal jaundice
How does severe disease present?
More severe disease causes in utero anaemia and, as this worsens, cardiac failure, ascites and oedema and fetal death may follow
Does rhesus disease get better in successive pregnancies?
No, it gets worse as maternal antibody production increases
How do you assess the severity of fetal anaemia?
Doppler US of the peak velocity in systole of the fetal middle cerebral artery has a high sensitivity for significant anaemia at least before 36 weeks
