Rhesus Incompatibility in Pregnancy

Question 1

Rhesus defintion

Answer 1

Various types of rhesus antigens on the surface of red blood cells. The antigens on the red blood cells vary between individuals. The rhesus antigens are separate to the ABO blood group system.

Question 2

Pregnant women that are rhesus-D positive

Answer 2

Do not need any additional treatment during pregnancy.

Question 3

Pregnant women that are rhesus-D negative

Answer 3

• If child is rhesus +ve. It is likely at some point in the pregnancy (i.e. childbirth) that the blood from the baby will find a way into the mother’s bloodstream.
• When this happens, the baby’s red blood cells display the rhesus-D antigen. The mother’s immune system will recognise this rhesus-D antigen as foreign, and produce antibodies to the rhesus-D antigen. The mother has then become sensitised to rhesus-D antigens.

Question 4

Sensitisation in first pregnancy

Answer 4

Sensitisation process does not cause problems during the first pregnancy.

Question 5

Sensitisation in subsequent pregnancies

Answer 5

The mother’s anti-rhesus-D antibodies can cross the placenta into the fetus. If that fetus is rhesus-D positive, these antibodies attach themselves to the red blood cells of the fetus and causes the immune system of the fetus to attack them, causing the destruction of the red blood cells (haemolysis). The red blood cell destruction caused by antibodies from the mother is called haemolytic disease of the newborn.

Question 6

Treatment

Answer 6

Prevention: IM anti-D injections to rhesus -ve
= There’s no way to reverse sensitisation process once it has occured so prophylaxis essential

Question 7

How does Anti-D meds work

Answer 7

By attaching itself to the rhesus-D antigens on the fetal red blood cells in the mothers circulation, causing them to be destroyed. This prevents the mother’s immune system recognising the antigen and creating it’s own antibodies to the antigen.

Question 8

When is anti-D given?

Answer 8

• 28 weeks gestation
• Birth (if the baby’s blood group is found to be rhesus-positive)

Question 9

When else should anti-D injections be given

Answer 9

Any time where sensitisation may occur, such as:
- Antepartum haemorrhage
- Amniocentesis procedures
- Abdominal trauma

Question 10

Kleinhauer test

Answer 10

Anti-D is given within 72 hours of a sensitisation event. After 20 weeks gestation, the Kleinhauer test is performed to see how much fetal blood has passed into the mother’s blood, to determine whether further doses of anti-D are required.

Question 11

How is Kleinhauers test performed

Answer 11

Adding acid to a sample of the mother’s blood.
- Fetal haemoglobin is naturally more resistant to acid, so that they are protected against the acidosis that occurs around childbirth.
- The number of cells still containing haemoglobin (the remaining fetal cells) can then be calculated.