Blood Groups and Rhesus Negative in Pregnancy: What Your Blood Type Means

Your blood group matters most at two key moments: if you ever need a blood transfusion, and if you are pregnant. If you are Rhesus negative, a simple injection during pregnancy can protect future babies.

Imagine your midwife telling you that you are “Rh negative” and need an injection called anti-D. You have never thought about your blood type before, and you wonder if something is wrong with you or your baby.

ABO blood groups

Your ABO blood group depends on whether your red blood cells carry A antigens, B antigens, both (AB) or neither (O). These are inherited from your parents.,Your plasma naturally contains antibodies against the ABO antigens you do not have. For example, people with group A have anti-B antibodies. This is why receiving the wrong blood group in a transfusion can cause a serious reaction.

The Rhesus (Rh) factor

The Rhesus D antigen is another protein that may be present on red blood cells. If you have it, you are Rh positive; if not, you are Rh negative. The proportion of people who are Rh negative varies between populations; it is relatively common in people of European descent and less common in many African and Asian populations.

Who can give blood to whom

• Group O negative red cells can be given to almost anyone in an emergency, which is why O negative donors are so valuable
• Group AB positive people can receive red cells from any group
• In practice, hospitals give blood of your own group, matched and checked carefully
• Plasma compatibility works the other way round: AB plasma can be given to anyone

Why Rhesus matters in pregnancy

If a Rhesus negative mother carries a Rhesus positive baby, some of the baby’s blood can enter her circulation, especially during birth, miscarriage, abdominal injury or certain procedures. Her immune system may then make anti-D antibodies.,These antibodies do not usually affect the current pregnancy, but in a future pregnancy with a Rhesus positive baby they can cross the placenta and attack the baby’s red blood cells. This is called haemolytic disease of the fetus and newborn, and it can cause anaemia, jaundice and, in severe cases, serious illness.

How anti-D prevents this

Anti-D immunoglobulin is an injection that stops the mother’s immune system from making its own anti-D antibodies. It is offered to Rhesus negative women at certain times in pregnancy, often as a routine dose around 28 weeks, after birth if the baby is Rhesus positive, and after events such as bleeding, miscarriage, abdominal injury or procedures like amniocentesis.,Some countries now offer a blood test in pregnancy that checks the baby’s Rhesus type from the mother’s blood (cell-free fetal DNA), so anti-D can be avoided if the baby is Rhesus negative too.

Antibody screening in pregnancy

All pregnant women are usually offered blood tests early in pregnancy, and often again at 28 weeks, to check blood group and look for antibodies that could affect the baby. If antibodies are found, the pregnancy is monitored more closely, sometimes with specialist scans.

Blood transfusion safety

• Before a transfusion, a blood sample is tested for your group and antibodies, and the blood is cross-matched
• At the bedside, staff check your identity carefully against the blood bag
• Tell staff immediately if you feel unwell during a transfusion: fever, shivering, rash, breathlessness or back pain
• Some people are given specially selected blood, for example after certain treatments or with rare antibodies

Becoming a blood donor

Blood services in every country rely on volunteer donors. If you are healthy and eligible, donating blood can save lives, and O negative donors are especially needed. Check your national blood service for eligibility rules.

Frequently asked questions

Can blood group change?

Not usually, except in rare situations such as after a bone marrow transplant.

Does my partner’s blood group matter?

For Rhesus, yes: if the father is Rhesus negative, the baby will also be Rhesus negative. Your midwife will advise.

Does blood type affect personality or diet?

There is no good evidence that blood type determines personality or the best diet.

But is the anti-D injection safe?

Anti-D is made from donated blood plasma and is screened and treated to reduce the risk of infections. It has been used safely for decades and has dramatically reduced serious harm to babies.

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Sources: NHS Blood and Transplant, World Health Organization blood safety, National Institute for Health and Care Excellence, Royal College of Obstetricians and Gynaecologists, American College of Obstetricians and Gynecologists.