Flashcards in Rhesus and allo immunisation Deck (23)
First antenatal visit steps?
-Alloimmunisation assessment (risk allocation, partner grouping)
-Booking (MFM subspecialist)
If heterozygous partner how to get foetal DNA to detect alloimmunisation?
Foetal DNA typing:
-free foetal DNA from maternal blood
Antenatal care for low risk isoimmunisation?
-Antibody titre at each visit (rises quickly if small foeto-maternal haemorrhage)
-Deliver at 38 weeks (avoid late pregnancy maternal -> foetal antibody transfer)
antental care for medium risk isoimmunisation?
-Antibody titre at each visit
-US from 20 weeks (MCA peak systolic velocity
-Cardiotocographs from 32 weeks
-Deliver 38w (or earlier if foetal anaemia)
Antenatal care for high risk isoimmunisation?
-US from 17 weeks
-Foetal blood sampling if MCA PSV increased
-Intrauterine transfusion (if foetal anaemia)
Screening for anti red cell antibodies in pregnancy?
-All at first antenatal visit
-Rh -ve additionally at 28w + delivery
How is immunisation prevented during blood transfusion?
-Rh (D) compatible
-Kell negative blood to women
How is immunisation due to foeto-maternal haemorrhage prevented?
Administration of passive anti D to Rh(D) negative women at times of sensitising events e.g.:
-bleeding in pregnancy (miscarriage, APH)
-trauma (amnio, CVS, MVA)
-routine at 28 and 34w
which parental antibody combination can lead to isoimmunisation of the mother?
RhD- woman is pregnant with foetus of RhD+ father which has inherited RhD
Which events may lead to maternal exposure to foetal RBCs?
-Delivery of the placenta
-Threatened, spontaneous or elective abortion
-Bleeding a/w placenta previa or abruption
-External cephalic vesion
What occurs if an RhD+ foetus is carried by a previously alloimmuised mother?
Anamnestic response of mother with production of IgG which freely cross placenta, enter foetal circulation, bind antigenic sites on foetal RBCs.
What happens to foetal RBCs bound by maternal antiD?
Haemolysed in the foetal reticuloendothelial system and destroyed via complement pathways
-if foetus can maintain RBC production may not develop anaemia
-if large numbers of RBCs destroyed, foetal anaemia may develop
What are the typical characteristics of the first affected rhesus pregnancy?
-elevated bilirubin at birth (UV light therapy, exchange transfusion)
What is the serious sequelae or markedly elevated bilirubin?
Kernicterus - deposition of bilirubin in basal ganglia producing permanent neuro symptoms or even death
Why does foetal oncotic pressure decrease with severe haemolysis?
Foetal haemotopoiesis increases resulting in extra medullary haemotpoiesis (i.e. liver). When liver produces RBCs, synthesis of other proteins decreases leading to lower oncotic pressure.
This + increased intravascular resistance to flow due to haematopoietic islands in liver can cause ascites, pleural effusion or s/c oedema
What is hydrops fetalis?
Fluid accumulation in at least two extravascular compartments (pericardial / pleural effusion, ascites, s/c oedema).
Why does hydrops fetalis occur?
1) anemia produces high output cardiac failure. Myocardial dysfunction results as CV attempts to keep pace with O2 demands. Effusions etc result due to hydrostatic increases.
2) anaemia itself can cause myocardial ischaemia, damaging myocardial function
Why is MCA PSV used to measure anaemia risk?
MCS PSV related to viscosity of blood. Less viscous if foetal anaemia therefore flow velocity increases. Compare to standard curves to estimate anaemia risk
When is AntiD indicated in an unsensitised Rh patient?
-time of procedures associated with potential bleeding i.e. amnio, CVS
-abortion of any kind
-within 72h delivery of Rh+ infant
-Conditions a/w haemorrhage i.e. trauma, abruptio placentae
-unexplained vaginal bleeding during pregnancy
What is the Kleihauer test?
If >30mL f-m haemorrhage potential, test identifies foetal RBCs in maternal circulation; ratio can be used to give correct AntiD dose
When is AntiD prophylaxis indicated?
-Sensitising events in first trimester (miscarriage, ectopic pregnancy, termination of pregnancy, CVS). 250IU IM RhD immunoglobulin (625IU for multiple gestations)
-Events in T2/T3: amniocentesis, cordocentesis, abdominal trauma sufficient to cause foetomaternal haemorrhage, external cephalic version or antepartum haemorrhage
-Routine adminisation at 28 and 34 weeks in addition to doses for sensitising events
-Post partum administration of 600IU is necessary within 72h
What is the rate of red cell antibody formation with anti d prophylaxis?
Prophylaxis reduces antibody formation to 0.2%