Information if you are pregnant and D negative blood group
This information is for you if you are pregnant and your blood test shows that you are D negative. It explains what being D negative means for you during your pregnancy and after your baby is born.
You will be offered a screening blood test called cell free fetal DNA (cffDNA). This test can predict your baby’s D blood group. Knowing your baby’s blood group helps your midwife provide the right care for you and your baby throughout your pregnancy.
What your blood test result means
Your blood group (your type of blood) will be one of the four main groups.
- Group O
- Group A
- Group B
- Group AB
Within each blood group, people are either D positive or D negative. Your blood test shows that you are D negative.
Why is it important to know I am D negative?
Knowing you are D negative means we can offer you a further screening test to check whether your baby is D negative or D positive.
Explaining your blood type
Your blood is made up of:
- red blood cells
- white blood cells, and
- platelets.
Red blood cells have markers on their surface called antigens. One of these is the D antigen.
- If the D antigen is present, your blood group is D positive.
- If it is not present, your blood group is D negative. Around 15% (15 in 100) of people are D negative.
Why does being D negative matter?
If your blood group is D negative and your baby is D positive and your baby’s blood mixes with yours, there is a chance your body may make anti-D antibodies.
Antibodies are part of your body’s way of protecting you against anything the body sees as unfamiliar. Anti-D antibodies can cross the placenta into your baby’s bloodstream and damage their red blood cells. This can make your baby unwell and sometimes they may need treatment in hospital.
Having anti-D antibodies is the most common cause of a rare condition called haemolytic disease of the fetus and newborn (HDFN).
About the cell free fetal DNA (cffDNA) test
As you are D negative, we will offer you another blood test, called cffDNA. This test looks at tiny amounts of your baby’s DNA that naturally pass into your blood. DNA is the genetic information found inside all cells.
If the test predicts your baby is D positive, we will offer you anti-D immunoglobulin injections (anti-D). Having anti-D injections greatly reduces the risk of HDFN.
If you choose to have cffDNA screening, your blood sample will be stored during your pregnancy and may be used to check the result following the birth of your baby. It may also be used for quality assurance purposes.
What will the cffDNA results be?
The test will give one of the following results.
Your baby is D positive.
- You will be offered anti-D injections.
Your baby is D negative.
- Anti-D injections will not be recommended.
The test result is unclear.
- In this case, you will be offered anti-D injections.
You can normally have this test from around your 16th week of pregnancy up to 26 weeks.
Your midwife will discuss with you when you will be offered the test and tell you when to expect your results.
What if my baby is predicted to be D positive?
You will have an appointment with your midwife at around 28 weeks of pregnancy. At this appointment:
- you will have a blood test to check for antibodies, and
- you will be offered an anti-D injection.
Anti-D helps to stop antibodies from developing if any of your baby’s blood has mixed with yours. This reduces the risk of HDFN.
What are anti-D injections?
Anti-D injections are made from plasma, which is the liquid part of blood that the blood cells float in as they move around the body. The plasma used to make anti-D is collected from carefully screened blood donors. It goes through several safety steps to remove germs and viruses, making it very safe.
Anti-D injections do not offer you lifelong protection. This means you may need them again in future pregnancies if you are carrying a baby who is D positive. Some people choose to have cffDNA screening, which can predict the baby’s D type and help decide whether anti-D is needed in that pregnancy.
How does anti-D work?
Anti-D works by removing any of your baby’s red blood cells which may have passed into your blood. This stops your body from making its own anti-D antibodies.
Is anti-D safe?
Yes. Anti-D is considered very safe.
- Some people feel mild pain when the injection is given into the muscle.
- Occasionally, some people can get a mild allergic reaction.
- The way anti-D is produced is strictly controlled, and donors are screened, so the risk of a known virus being passed on is very low.
Other reasons why you may need an anti-D injection
Please contact your midwife or your hospital doctor (obstetrician) as soon as possible if you:
- have any bleeding in pregnancy, or
- injure your abdomen (for example, from a fall or a seat belt in a sudden stop).
In these situations, there is a chance that some of your baby’s red blood cells could pass into your bloodstream. If this happens and your baby is D positive, you may need an anti-D injection to reduce the chance of antibodies developing.
What if my baby is D negative on the cffDNA test?
If the test shows your baby is D negative, they are likely to have the same D group as you. In this case, anti-D injections will not be recommended.
How accurate is the cffDNA test?
The test is 99.9% accurate (999 in 1000) at correctly predicting a baby’s D blood group.
Should I have the cffDNA screening test?
Taking part in screening is your choice. If you decide not to have the cffDNA test, we recommend you have anti-D injections, because around 60% (60 in 100) of babies whose mothers are D negative will be D positive.
If you would like more help understanding this information, please speak to your midwife or obstetrician.
What if the results are not clear?
Sometimes the test cannot tell your baby’s D group. If this happens, we will offer you anti-D injections to be safe. This reduces the chance of antibodies developing and making your baby unwell.
What if I am pregnant with more than one baby?
You can have the test if you are pregnant with twins. The test is just as accurate as it is for women having one baby.
- If one or both babies are D positive, we will offer you anti-D injections.
- If both babies are D negative (the same as you), anti-D injections are not recommended.
- If you are pregnant with more than two babies, we will not offer you the test. We will recommend you have anti-D injections, because we cannot tell what D group the babies are.
What happens when my baby is born?
After your baby is born, your midwife will take a small blood sample from you and a sample from the umbilical cord. These tests confirm whether your baby’s blood group is D positive or D negative.
What happens if my baby’s D group is different from what the test predicted?
In around 0.1% of cases (1 in 1000), the test will predict that your baby is D negative, but testing after birth will show the baby is D positive.
If a woman who is D negative has a baby who is D positive and did not have anti-D in pregnancy, she may become ‘sensitised’.
This happens when some of the baby’s red blood cells mix with the mother’s blood, and her body makes anti-D antibodies.
If this happens, you may be offered anti-D after your baby is born. This is because the birth is when your baby’s blood is most likely to mix with yours. If antibodies are found in your blood in your next pregnancy, you will be closely monitored and may need specialist care to keep you and your baby safe.
What if I attend a different hospital?
Hospitals in Wales follow the same antenatal screening pathway. Hospitals outside of Wales may follow different policies. You will be told about any differences if you receive care outside of Wales. Please show the hospital staff your test results, which will be in your maternity record.
Where can I get more information?
NHS 111 Wales – Health A-Z : Blood groups