Rhesus Negative Test

Your Baby's Blood Group and Anti D

In all pregnancies the mother’s blood group is checked. Should the mother be Rhesus Negative (15% chance in white Europeans) and the father be Rhesus Positive (85% chance in white Europeans) then the baby has a 66% chance of being Rhesus Positive and 33% chance of being Rhesus Negative. If the mother is Rhesus Negative and the baby is Rhesus positive, then there is a small chance that baby’s blood cells can cross to the mother’s circulation and set up an antibody response which can cross back and damage the baby. This can be prevented by giving all mothers an injection of Anti D immunoglobulin. This is manufactured safely from human blood products. However, in 33% of cases the injection is unnecessary.

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The routine injection for all mothers has been necessary because until recently it was difficult to know the baby’s blood group when still in the womb. The technology which gives us NIPT (Non-Invasive Prenatal Testing) for Down’s syndrome is also used, by a different laboratory, for NIPT to determine the baby’s blood group. This is done by taking a simple blood sample from a vein in the mother’s arm and sending it to a specialised laboratory. Within a few days the mother will be advised of the baby’s blood group. Should it be Rhesus Negative then nothing more needs done, and you do not require the Anti D injections. Should the baby be Rhesus Positive you will need to discuss the need for an Anti D injection with a midwife. The NHS accept these results. In fact, the test is done in an NHS laboratory although it is generally not available in NHS care.

How and when will I receive my results?

The blood sample is processed by an NHS laboratory and the results take between 10 and 14 days. We will email the results to you. This laboratory report should then be added to your primary care notes e.g your NHS pregnancy records.

What happens if the result is D negative?

If your unborn baby is predicted to be D negative, please discuss the results with your primary care midwife who will recommend that you do not have anti-D injections before or after giving birth. However, there is a very small chance (0.1%) that the baby might be found to be D positive once born. In this case you are likely to be offered an anti-D injection at that time by your NHS Hospital.

What happens if the result is D positive?

The Rhesus blood test is predictive, with a positive predictive value of 98%. This means that we would expect 98 out of 100 babies with a predictive positive result to be confirmed as D positive after birth, however, 2.0% (2 out of 100 babies) may in fact be D negative.

If your blood test report predicts that your unborn baby is D positive, or the result is inconclusive, your primary care team will offer an anti-D injection. This is of no concern as anti-D prophylaxis would have been offered in all cases if DNA testing had not taken place and the injection will not harm your baby.

For more information: Rhesus disease - Prevention

Important Patient Information

       The test is performed from 12 weeks of pregnancy. If you have not had a scan with us in the pregnancy, please ensure that you bring your latest pregnancy scan report and your NHS or Hospital number along with you. The sample will not be accepted by the laboratory without these patient identification references.

Our team are very experienced in blood draws, however there are many factors which can affect the success of a blood draw. Please ensure you are well hydrated and warm at the time of your appointment. If you are anxious, you may find some meditation useful. If our team are unable to draw your sample, we may require you to attend the laboratory in the basement of the building or the TDL laboratory which is a short walk from the clinic. On some occasions we may require you to return at a different time to draw the sample. We always aim to provide the highest levels of care with the least inconvenience, however clinical procedures in nature vary from patient to patient.

The Birth Company always ensure that Rhesus Blood Test samples are couriered at the earliest possible time, any delays and test failures are communicated to patients at the earliest opportunity. TBC does not accept responsibility for delays and test failures. 

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Ground Floor,
32 Wimpole Street
London W1G 8GT

Nearest Underground Tube Stations

Bond Street
Oxford Circus

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Alderley Edge Medical Centre, Talbot Road, Alderley Edge,
Cheshire, SK9 7HR

Nearest Overground Train Station Alderley Edge

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Wimpole Street, London

The Birth Company
Ground Floor
32 Wimpole Street

020 7725 0528
[email protected]

Wimpole Street, London Opening Times

Mon 08:00 - 20:00
Tue 08:00 - 20:00
Wed 08:00 - 20:00
Thu 08:00 - 20:00
Fri 08:00 - 18:00
Sat 09:00 - 16:00
Sun 10:00 - 14:00

Alderley Edge, Cheshire

The Birth Company
Alderley Edge Medical Centre,
Talbot Road,
Alderley Edge

01625 70 40 80
[email protected]

Alderley Edge, Cheshire Opening Times

Mon 09:00 - 17:00
Tue 09:00 - 17:00
Wed 09:00 - 17:00
Thu 09:00 - 17:00
Fri 09:00 - 17:00
Sat 09:00 - 16:00 (On selected dates)
Sun Closed
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