At a glance
Why get tested?
To determine the ABO and RhD blood group, and any possible blood group (commonly referred to as red cell antibodies), that may affect pregnancy and cause . HDN occurs when red cell antibodies present in the mother’s bloodstream cross the placenta and destroy the unborn baby’s red cells. This may lead to serious complications such as severe anaemia, brain damage and sometimes death of the baby. Early identification and detection helps maternity carers to support a pregnancy plan tailored for safe care and management of both the mother and the baby.
When to get tested?
As part of the routine antenatal care provided by a midwife or doctor. The first blood test is normally taken during the first trimester (12-16 weeks), with any subsequent blood tests as directed by the lead maternity carer.
If a woman is RhD negative, she may require an injection of anti-D (also known as Rh (D) ) during pregnancy and/or after delivery. Her lead maternity carer will advise if, and when, these injections are required. If anti-D is required, the blood sample for the 28 week antibody screen must be taken before the injection is given.
A blood sample drawn from a vein in the arm.
Frequency of testing?
This depends on results from the first antenatal tests. If the woman is RhD negative, a further antibody screen will be taken at 28 weeks. If a blood group antibody is identified, frequent blood tests may be required during the pregnancy.
Test preparation needed?
What is being tested?
All pregnant women are screened and reviewed during their pregnancy to establish their ABO and RhD blood group and identify if there are any red cell antibodies in their blood. This forms part of the routine screening during the antenatal period.
Blood groups are present on the surface of red blood cells, the two most commonly known and important blood groups are ABO and Rh (previously called Rhesus). There are also many other blood groups on the cells. These are all passed from parents to children, and can differ between people. It is the difference between people that can affect a pregnancy. If the blood group of the mother is different to that of the baby the mother may make an against the baby’s red blood cells. This antibody can cross the placenta and rapidly destroy the baby’s red cells, resulting in . Screening for the presence of red cell antibodies is therefore very important to protect the baby from HDN.
How is the sample collected for testing?
The test is performed on a blood sample taken by a needle placed in a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
The antenatal group and screen is used by a midwife or doctor to:
- Establish the mother’s ABO and RhD blood group
- Identify those women who are RhD negative and may require anti-D injections during pregnancy and after delivery
- Identify women at risk of having babies affected by and predict the risk to the baby by screening for any red cell antibodies.
If antibodies are detected the doctor or midwife will continue to monitor the level () of antibody in the mother’s blood by regular blood sampling during pregnancy. The results of these tests guide the lead maternity carer on appropriate treatment to protect the baby from potential damage caused by the blood group antibody crossing the placenta causing HDN.
In the most severe cases of HDN the baby may die or be born with severe anaemia and/or severe damage caused by high levels of bilirubin ().
When is it requested?
- The first blood test should be taken during the first trimester of pregnancy
- If the mother is RhD negative a further test should be taken at 28 weeks before the anti-D injection is given
- Further tests (frequency) are determined by the midwife or doctor and depend on the previous test results. If a woman has a blood group antibody, frequent testing may be required to keep both mother and baby safe during pregnancy.
What does the test result mean?
If the mother is RhD negative anti-D injections may be required during pregnancy and after delivery. Her lead maternity carer will advise if, and when, these injections are required.
If a blood group antibody is detected, regular blood tests are required during pregnancy to monitor for HDN.
Last Review Date: May 23, 2022
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