Summary

• All pregnant women are offered tests at their first antenatal check-up that identify their blood type and check the Rhesus (RhD) factor in their blood.
• These tests will show what blood type they have and whether they are RhD-negative or RhD-positive.
• If you are RhD-negative and your baby is RhD-positive, this can harm the baby by causing a complication called haemolytic disease of the foetus and newborn (HDFN), a condition where the baby’s red blood cells are attacked by the mother’s immune system.
• Only RhD-negative women and their babies are at risk.
• However, treatment is available. If you are RhD negative, you can be given injections of RhD immunoglobulin (known as Anti-D) to prevent your immune system from developing antibodies.

What are blood groups and why are they important?

Your immune system protects you by making antibodies to attack substances that should not be in your body and could be harmful to you. This includes infections like viruses and bacteria as well as toxic substances. It does this by targeting special markers called antigens which are found on the surfaces of most cells.

Your blood cells have marker antigens on their surface. Blood is made up of different cells including red blood cells, white blood cells and platelets suspended in a liquid called plasma.

The surface of every red blood cell is coated with these marker antigens. Everyone has their own set of antigens which are inherited from their parents. There are about 30 blood group types, but A, B, AB and O are the most common.

Blood groups

Rhesus D (RhD) factor

Each of these blood types is then further grouped according to whether your red blood cells have the Rhesus D (RhD) marker antigen, also known as RhD factor.

If you are RhD-positive your blood cells have RhD antigens. If you are RhD-negative, your blood cells do not have the RhD antigen.

Why get tested?

As a normal part of pregnancy screening, it will be important to find out your blood group type and whether you are RhD positive or negative.

Blood cells with marker antigens that are different from your own can be attacked by your immune system.

If you are RhD-negative and the father of your baby is Rh-positive your baby can inherit RhD-positive blood from their father.

In this situation, your immune system can attack the baby’s blood by making anti-RhD antibodies. These antibodies destroy red blood cells that are different from your own. Your immune system sees the baby’s RhD-positive cells as foreign. This is called RhD incompatibility.

RhD incompatibility is not common. Most people are RhD-positive and only those pregnant women who are RhD-negative are at a risk.

First or subsequent pregnancy?

RhD incompatibility is usually not a problem if this is your first pregnancy. This is because your baby's blood would not normally enter your own blood system. It is during the birth that your baby’s blood is most likely to mix with yours.

In this first pregnancy and you and your baby are RhD incompatible, your body does not have a chance to make a lot of antibodies and so there will be no issues. However, if treatment is not given and if in future you carry another baby with different RhD factor to your own, your antibodies may recognise your baby's blood cells as foreign and attack those cells.

Haemolytic disease of the fetus and newborn

The condition in which the baby’s RhD-positive red blood cells are attacked and destroyed is called haemolytic disease of the fetus and newborn (HDFN).

This is serious type of anaemia in which the baby’s red blood cells are destroyed faster than the body can replace them.

In severe cases of HDFN, the baby may be born with anaemia, jaundice, heart failure or even be still born. To ensure that these issues do not arise, an antenatal group and screen is used to:

• Establish your blood group and RhD factor.
• Find out if you are RhD-negative and will need RhD immunoglobulin (anti-D) injections during pregnancy and after delivery.
• Find out if you are at risk of having a baby affected by HDFN and predict the risk to the baby by screening for and monitoring any red cell antibodies.

Having the test

Sample

Blood.

Any preparation?

None.

Your results

Treatment

If antibodies are found, your medical team will monitor your pregnancy to reduce any risk. You will be given RhD immunoglobulin (known as Anti-D) injections to prevent your immune system from developing antibodies:

• During your pregnancy to protect your baby from the antibodies.
• After delivery of the baby to neutralise the effect of any of the baby’s red cells in your circulation.

Once you have red blood cell antibodies, they stay with you for life.

Other antibodies

Other antibodies may also develop if you and your baby have different blood group antigens. These need to be found and may also be monitored during your pregnancy if the antibody present can cause HDFN.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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