Rhesus alloimmunisation

Question 1

What is the pathophysiology of Perinatal iso- immune disorders?

Answer 1

• Mother exposed to an antigen
• Mother produces an antibody
• Antibody crosses the placenta
• Fetal sequelae

There are less common cases where the antibodies are directed against white cells or platelets.

Question 2

What is the screening schedule for those with anti-red blood cell antibodies?

Answer 2

• All women are screened for anti red blood cell antibody on their first visit
• Those that are negative are rescreened at 28 weeks

Question 3

What is a maternal auto-antibody?

Answer 3

• Antibody against an antigen the mother has herself. Autoimmune disease in the mother as well

Question 4

What is a maternal alloantibody?

Answer 4

-Antibody against an antigen the mother does not have, causes no problems in the mother

Question 5

Name 3 types of maternal autoantibody diseases

Answer 5

• Thyroid autoimmune disease: Graves, Hashimotos
• Connective tissue diseases: SLE
• Immune thrombocytopaenic purpura

Question 6

Name three types of maternal alloantibodies

Answer 6

• Red cell alloimmunisation
• Perinatal alloimmune thrombocytopaenia
• Perinatal Alloimmune Neutropaenia

Question 7

Is it IgG or IgM which readily crosses the placenta?

Answer 7

IgG

Question 8

Describe the specific pathology of red cell isoimmunisation?

Answer 8

In red cell isoimmunisation, the fetus has red cell antigens that the mother does not possess. The mother is able to make an anti-red blood cell antibody that does not affect her but can cause haemolysis in the fetus.

Question 9

What are red cell antigens which are common and most harmful? Which ones are associated with haemolytic disease of the fetus?

Answer 9

• Rhesus antigen D, c, E, C
• Kell, Kidd, Duffy
• M, N, S, s

Question 10

True or false, the fetal blood cells produce lewis antigen?

Answer 10

False

Question 11

How does the mother begin to make antibodies against these red cells?

Answer 11

• Blood transfusion

- Fetomaternal haemorrhage

Question 12

How does blood transfusion lead to the production of autoantibodies?

Answer 12

Blood Transfusion: Although blood administered is ABO and Rh Group compatible, there is generally no matching for all the other red cell antigens. This will serve as a primary immune stimulus and antibody production will be initiated.

Question 13

Fetomaternal haemorrhage what is it? How is it caused?

Answer 13

Blood Transfusion: Although blood administered is ABO and Rh Group compatible, there is generally no matching for all the other red cell antigens. This will serve as a primary immune stimulus and antibody production will be initiated.

• Bleeding: Abortion, Ectopic, APH
• Trauma: CVS, Amniocentesis, Version, Motor Vehicle Accident
• Delivery
• Occult bleeding

Question 14

What is the incidence of Red cell immunisation in pregnancy?

Answer 14

Incidence is 1% of all pregnancies
85% are due to Anti-D
15% due to other (Kell, c,E, Fya)

Question 15

Transfer of antibodies from mother to the placenta is minimal prior to 16 weeks of gestation. True or False?

Answer 15

True, transfer of antibody across the placenta increases as gestation advances and is minimal before about 16 weeks gestation. In late pregnancy there is a surge of antibody transfer to equip the neonate with antibodies to fight infection.

Question 16

What is the clinical presentation or consequences of anti-red blood cell isoantibodies?

Answer 16

• Breakdown of fetal erythrocytes with two consequences
• Accumulation of unconjugated bilirubin in the neonatal period can lead to development of kernicterus
• Accelerated haemolysis will not be able to keep up with the rate of haemolysis and anaemia will occur, where anaemia is severe the fetus will develop congestive cardiac failure with widespread accumulation of fluid subcutaneously and in peritoneal pleural and pericardial cavities (FETAL HYDROPS)
• Further haemolysis may cause fetal death in utero

Question 17

How is the severity of Red cell isoimmunisation predicted by antibody titre?

Answer 17

Mild: Ab titre < 32
Moderate: Ab titre between 64-256
Severe: Ab titre > 512

Question 18

What therapy is given if there is occult feto-maternal haemorrhage?

Answer 18

• Prevention immunisation
• Prophylactic anti -d at 28 & 34 weeks
• Prophylaxis prevents 90%

Question 19

What is the importance of partner grouping in the ante-natal visit?

Answer 19

• If partner does not have the relevant antigen
• Able to completely reassure the couple
• Return to normal risk
• Return to normal mode of care

Question 20

If the partner is heterozygous, how do you determine if the fetus has big D?

Answer 20

• We can type the fetus or fetal blood based on DNA leaked by fetal placenta into the maternal circulation.

Question 21

How do we prevent the development of anti-D antibodies?

Answer 21

• Passive administration of anti-D, binds to the D antigen on the fetal red cells, prevents recognition by the fetal red cells and prevents recognition by the maternal immune system, therefore preventing primary immunisation as a consequence of fetomaternal haemorrhage
• The other anti’s are not passively administered because it is not cost effective