Red cell isoimmunisation

Question 1

What is red cell isoimmunisation?

Answer 1

Production of antibodies in response to an isoantigen present on an erythrocyte

Question 2

When does maternal isoimmunisation occur?

Answer 2

When the mothers immune system is sensitised to antigens on fetal erythrocytes, resulting in the production of Ig antibodies

Question 3

What can happen in subsequent pregnancies after maternal isoimmunisation?

Answer 3

Antibodies can cross the placenta and attack the fetal red blood cells - leading to haemolysis and anaemia

Question 4

What is the disease in the newborn resulting from isoimmunisation called?

Answer 4

Haemolytic disease of the newborn

Question 5

When might a sensitising event occur?

Answer 5

Antepartum haemorrhage
Abdominal trauma
Delivery

Question 6

Which blood group is the most common for mothers to experience isoimmunisation?

Answer 6

Rhesus D negative blood group women with Rhesus D positive foetus

Question 7

Describe Rhesus D isoimmunsation

Answer 7

RHD- woman and RhD+ Man, RhD+ foetus

During childbirth, woman comes into contact with the foetal RhD+ blood and anti-D antibodies are produced

She later becomes pregnant with a second RhD+ child

The womans anti-D antibodies cross the placenta during this pregnancy and enter the foetal circulation which contains RhD+blood. They bind to the foetus RhD antigens on its erythrocytic membranes

Causes the foetal immune system to attack and destroy its own RBCs (haemolytic disease of newborn) leading to foetal anaemia

Question 8

What can be given to prevent isoimmunisation if a sensitising event has occurred?

Answer 8

Anti-D immunoglobulin

Question 9

Describe how anti-D immunoglobulin works

Answer 9

Binds to any RhD+ cells in the maternal circulation and no immune response is stimulated

Question 10

Give the indications for Anti-D immunoglobulin use

Answer 10

In RhD-ve women after any sensitising event:
Invasive obstetric testing (amniocentesis or chorionic villus sampling)
Antepartum haemorrhage
Ectopic pregnancy
External cephalic version
Fall or abdominal trauma
Intrauterine death
Miscarriage
Termination of pregnancy
Delivery - normal, instrument or c-section

Question 11

What are the two main blood tests considered following a sensitising event?

Answer 11

Maternal blood group and antibody screen

Question 12

Describe the feto-maternal haemorrhage test

Answer 12

assess how much foetal blood has entered the maternal circulation and if there has been a sensitising event after 20 weeks gestation the test is used to determine how much anti-D immunoglobulin should be administered

Question 13

How long after the sensitising event is IU given?

Answer 13

Up to 72hrs

Question 14

How much IU is given?

Answer 14

Depends on the gestation, time of sensitising event and the FMH value

Question 15

At what gestation are all RhD-ve women offered anti-D IU

Answer 15

28 and 34 weeks

Question 16

When are the maternal blood group and antibody screening tests performed?

Answer 16

At the booking visit (8 to 12 weeks gestation) and repeated at 28 weeks