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The anti-D injection is given during pregnancy to prevent rhesus disease between mother and baby. Rhesus disease can occur if a baby has a different type of rhesus blood group to their mother. It is rare that rhesus disease occurs during the first pregnancy as it is more frequently seen in subsequent pregnancies. To understand the anti-D injection, we first need to look at the different types of blood groups.
Blood group information is genetic, meaning that it is inherited from our parents. We are all typed into blood groups A, AB, B or O based on the type of antigens, or markers that there are on the surface of our blood cells. This is known as the ABO blood group. The second most important blood grouping is the rhesus or Rh group.
Rhesus blood grouping
At its simplest level, the rhesus factor (which is also known as the D antigen, or marker) is either present or not on the surface of our red blood cells. Whatever your ABO blood group is, this has no impact on whether you are Rh D positive or Rh D negative. As an example, you could be blood group A Rh D positive or A Rh D negative. In the UK approximately 84% of the population is Rh D positive and the remaining are Rh D negative.
Rh D negative used to be more commonly known as Rh negative, while Rh D positive was known as Rh positive. Whether a baby is Rh D negative or Rh D positive depends on the blood groups of the parents.
Being Rh D positive or Rh D negative does not usually cause any problems, unless you are Rh D negative and your unborn baby is Rh D positive.
Rhesus blood groups and pregnancy
In 1939 two doctors published details of a disorder called haemolytic disease of the newborn. This was one of the first indications that there could be an incompatibility of the blood between the baby and its mother.
If blood cells from an Rh D positive baby move into the blood stream of an Rh D negative mother then an immune response or sensitisation starts. The mother begins to produce antibodies (these tell the rest of the immune system to 'attack') against the D antigen on the surface of the baby's blood cells. These antibodies produced by the mother are known as anti-D antibodies.
Once the mother has produced anti-D antibodies they can then move into the baby's blood stream resulting in the small possibility of harm to the baby.
The Coombs test (or antiglobulin test) is used to check Rh D negative mothers early in the pregnancy, often at the start of antenatal sessions. Another type of Coombs test (direct) is used to show whether the mother has produced any antibodies that have travelled to the baby's blood stream.
What can high levels of anti-D antibodies cause?
Around 500 babies develop 'haemolytic disease of the foetus or newborn' or rhesus disease in England and Wales every year. Symptoms of this include jaundice and hypoglycaemia. It is rare that these problems occur in the first pregnancy, but subsequent pregnancies increase the risk of anti-D antibodies being produced, especially as during delivery there is a high chance that blood from the baby will become mixed with the mother's. There is also a small risk of blood mixing for unknown reasons or during amniocentesis. If you are Rh D negative you will be offered an anti-D injection after any of these events, if you experience any minor bleeding during pregnancy, or if you receive an injury to your abdomen.
Do I have to have the anti-D injection?
The anti-D injection will 'neutralise' any Rh D positive antigens that have entered the mother's blood. This will then prevent antibodies against the Rh D positive antigens from being produced.
You will only need the injection if you are Rh D negative and your unborn baby or newborn baby is Rh D positive.
You have to consent to having the anti-D injection, so ultimately it is your decision whether you chose to have the injection or not.
You may decide not to have the injection if after birth your baby is grouped as Rh D positive and you are certain that you will not become pregnant again.
Around 40% of Rh D negative mothers give birth to an Rh D negative baby and so do not need the anti-D injection.
Are there any side effects of the anti-D injection?
There is a small chance that you may develop a rash or flu-like symptoms. These injections have been offered for over forty years so plenty is known about them.
It is also recommended that you stay at clinic for around 20 minutes after the injection to make sure that you do not have an allergic reaction.
What are the risks to my baby?
The anti-D injection will not cause any harm to your baby.
What is the anti-D injection made from?
The anti-D injection is made from human blood plasma that is received through blood donation services. The chance of viruses being transmitted through anti-D injections is minute as all donors are screened for viruses and the blood is imported from countries that are CJD free.
When do I have the anti-D injection?
Routine antenatal anti-D prophylaxis (RAADP) is the long name for the anti-D injections that are given routinely through pregnancy. Prophylaxis means prevention.
The anti-D injection will be recommended if you are Rh D negative and routine tests show that you have not started to produce antibodies (or been sensitised) against Rh D positive antigens.
If you are Rh D negative you will be offered an antenatal anti-D injection at around 28 weeks and another anti-D injection after delivery (usually within 72 hours) if a Rh D positive baby is delivered.
Your baby's blood grouping
Your baby's blood will be tested after birth, usually with a sample from the umbilical cord. If you still do not know what your baby's blood group is when you leave the hospital, make sure you or a partner is aware of how to follow this up, especially if you will need the anti-D injection.
If your baby is Rh D positive and you have not produced any antibodies against the D antigen then you will be offered the injection within 72 hours of delivery. This decreases the chance of your next baby having rhesus disease.
What happens if a mother is already producing anti-D antibodies?
If the mother has already started to produce antibodies against their baby's antibodies then the anti-D injection is of no benefit. Instead they will have to have regular blood tests and scans and be monitored closely by their health professionals.
In summary, if you are an Rh D negative mother and your developing baby is Rh D positive then even though this may not cause problems during this pregnancy, be aware that any future pregnancies can increase the risk of rhesus disease. If you are Rh D negative and you have concerns about having the anti-D injection then you must speak to your health professionals as soon as possible.