Red Blood Cell Isoimmunisation Flashcards
what is the definition of red blood cell isoimmunisation
Where the mother mounts an immune response to the foetal red blood cells in her bloodstream, causing an immune response that crosses the placenta and destroys the foetal RBCs in utero
what determines rhesus type
3 linked gene pairs, of 2 alleles each
C/c
E/e
D/d
what is the most significant subtype of rhesus
D, as it determines +/-
what is the allele pair associated with rhesus +ve patients
DD, or Dd
how does rhesus sensitisation occur in pregnancy
Normally the first rhesus +ve child of a rhesus –ve mother does not get affected, as the mother needs time to recognise and develop antibodies to the foreign D antigen
This means that by the time the second child is present, the immune system is alread ‘sensitised’ to the antigen, meaning it can attack straight away
what is the major cause of jaundice <24 hours in a newbord
haemolytic anaemia related to rhesus incompatibility
what is the treatment for rhesus incompatibility
Anti-D immunoglobins at 28 weeks + during any sensitising events
what are examples of sensitising events in rhesus disease
Miscarriage
Threatened miscarriage
Uterus instumentation
Termination of pregnancy
Ectopic pregnancy
Amniocentesis
ECV
Foetal death
Antepartum haemorrhage
what happens after delivery with patients with rhesus incompatibility
Postnatally the foetuses blood type is also checked, if rhesus D +ve then anti-D is given, to the mother within 72 hours
A ‘kleihauer’ test is also performed within 2 hours to assess the number of foetal red cells in the maternal blood stream in order to assess if there is a bigger haemorhage, and if the anti-D dose needs increasing
how does rhesus disease manifest
Haemolytic disease
Mild disease
Neonatal jaundice
Neonatal anaemia
Severe disease In utero anaemia Cardiac failure Foetal hydrops Ascites Foetal death
The disease usually worsens with every pregnancy
what are the principles of management for rhesus disease
Identification of at risk women
Assessing foetal anaemia
Treating any disease
how are rhesus-ve women identified
Unsensitised women are screened at booking and 28 weeks for antibodies, if any are found the foetues genotype must be determined
Mothers with antibody levels of >4IU/ml are investigated for foetal anaemia using ultrasound
However if the mother has no history of previous issues, any reading <10IU/ml is unlikely to indicate anything serious and just requires regular follow every 2-4 weeks
Antibodies are less predictive for cases where there is previous dysfunction
how is foetal anaemia screened for
Pregnancies at risk of anaemia are screened using USS
This has a high sensitivity before 36 weeks
The scan is a doppler of the velocity of the MCA
Very severe anaemia (<5g/dl) is detected by foetal hydrops/foetal fluid and if visualised this needs to be screened for by testing the foetal blood - This is done via USS guided umbilical vein venopuncture
How is foetal anaemia treated
Transfusion treats any anaemia but this needs regular quantification and repeats – until about 36 weeks
Blood can be administered to the neonate also, anaemia tends to be treated with a top up whereas hyperbilirubinaemia from massive haemolysis requires an exchange transfusion
All neonates born to a Rhesus –ve woman must be checked for blood typing and any isoimmunisation
