Rhesus and allo immunisation

Question 1

First antenatal visit steps?

Answer 1

• Confirm pregnancy
• Gestational age
• Routine screening
• Alloimmunisation assessment (risk allocation, partner grouping)
• General advice
• Booking (MFM subspecialist)

Question 2

If heterozygous partner how to get foetal DNA to detect alloimmunisation?

Answer 2

Foetal DNA typing:

• amniocentesis
• free foetal DNA from maternal blood

Question 3

Antenatal care for low risk isoimmunisation?

Answer 3

• Antibody titre at each visit (rises quickly if small foeto-maternal haemorrhage)
• Deliver at 38 weeks (avoid late pregnancy maternal -> foetal antibody transfer)

Question 4

antental care for medium risk isoimmunisation?

Answer 4

• Antibody titre at each visit
• US from 20 weeks (MCA peak systolic velocity
• Cardiotocographs from 32 weeks
• Deliver 38w (or earlier if foetal anaemia)

Question 5

Antenatal care for high risk isoimmunisation?

Answer 5

• US from 17 weeks
• Foetal blood sampling if MCA PSV increased
• Intrauterine transfusion (if foetal anaemia)

Question 6

Screening for anti red cell antibodies in pregnancy?

Answer 6

• All at first antenatal visit

- Rh -ve additionally at 28w + delivery

Question 7

How is immunisation prevented during blood transfusion?

Answer 7

• Rh (D) compatible

- Kell negative blood to women

Question 8

How is immunisation due to foeto-maternal haemorrhage prevented?

Answer 8

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
• post delivery

Question 9

which parental antibody combination can lead to isoimmunisation of the mother?

Answer 9

RhD- woman is pregnant with foetus of RhD+ father which has inherited RhD

Question 10

Which events may lead to maternal exposure to foetal RBCs?

Answer 10

• Childbirth
• Delivery of the placenta
• Threatened, spontaneous or elective abortion
• Ectopic pregnancy
• Bleeding a/w placenta previa or abruption
• Amniocentesis
• Abdo trauma
• External cephalic vesion

Question 11

What occurs if an RhD+ foetus is carried by a previously alloimmuised mother?

Answer 11

Anamnestic response of mother with production of IgG which freely cross placenta, enter foetal circulation, bind antigenic sites on foetal RBCs.

Question 12

What happens to foetal RBCs bound by maternal antiD?

Answer 12

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

Question 13

What are the typical characteristics of the first affected rhesus pregnancy?

Answer 13

• mild aenamia

- elevated bilirubin at birth (UV light therapy, exchange transfusion)

Question 14

What is the serious sequelae or markedly elevated bilirubin?

Answer 14

Kernicterus - deposition of bilirubin in basal ganglia producing permanent neuro symptoms or even death

Question 15

Why does foetal oncotic pressure decrease with severe haemolysis?

Answer 15

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

Question 16

What is hydrops fetalis?

Answer 16

Fluid accumulation in at least two extravascular compartments (pericardial / pleural effusion, ascites, s/c oedema).

Question 17

Why does hydrops fetalis occur?

Answer 17

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

Question 18

Why is MCA PSV used to measure anaemia risk?

Answer 18

MCS PSV related to viscosity of blood. Less viscous if foetal anaemia therefore flow velocity increases. Compare to standard curves to estimate anaemia risk

Question 19

When is AntiD indicated in an unsensitised Rh patient?

Answer 19

• ~28w gestation
• time of procedures associated with potential bleeding i.e. amnio, CVS
• after ectopic
• abortion of any kind
• within 72h delivery of Rh+ infant
• Conditions a/w haemorrhage i.e. trauma, abruptio placentae
• unexplained vaginal bleeding during pregnancy

Question 20

What is the Kleihauer test?

Answer 20

If >30mL f-m haemorrhage potential, test identifies foetal RBCs in maternal circulation; ratio can be used to give correct AntiD dose

Question 21

When is AntiD prophylaxis indicated?

Answer 21

• 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

Question 22

What is the rate of red cell antibody formation with anti d prophylaxis?

Answer 22

Prophylaxis reduces antibody formation to 0.2%

Question 23

What are the contraindications for anti D prophylaxis?

Answer 23

• RhD positive or Du positive individual

- RhD negative or Du negative individual previously sensitised to RhD