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What does my blood type mean for my pregnancy?

Find out all you need to know about what yours and your partner's blood type means for your pregnancy.
You may have never given your blood type a second thought till now, but knowing whether you and your partner are rhesus negative or positive is important during your pregnancy.

This is because both your blood types, as mother and father of your baby, will have an effect on your baby's blood type. In most cases this simply means that baby inherits mum's or dad's blood type just as they inherit eye colour, and there's no cause for concern - however in certain cases there are extra things to consider.

What is my blood type?

Your blood type will either be A, B, AB, or O, and either rhesus negative or rhesus positive. If you don't know what yours is already, you'll find out at your ante-natal appointments, when your doctor will give you a blood test.

If you fit into any of the following scenarios then you've no need to worry:
  • You are rhesus negative and your partner is rhesus negative.

  • You are rhesus positive and your partner is rhesus positive.

  • You are rhesus positive and your partner is rhesus negative.
However if you are rhesus negative and your partner is rhesus positive, it's possible that your baby will inherit your partner's blood group and be rhesus positive. This can have consequences for your pregnancy if your baby's rhesus positive blood comes into contact with your rhesus negative blood.

Why does my blood type matter?

If you are rhesus negative and your baby is rhesus positive, your immune system may react against the presence of rhesus positive blood cells if it comes into direct contact with them. This is because your body would see this new type of blood as foreign and therefore may try to fight it.

If some of your baby's rhesus positive blood gets into your own bloodstream, your immune system will produce antibodies to try to combat this. Though this is unlikely to affect a current pregnancy, it could have consequences for future pregnancies because these antibodies will stay in your system.

If antibodies are in your system and you are pregnant in the future with a rhesus positive baby, these antibodies may cross the placenta and could cause baby to develop jaundice or anaemia. This is known as Haemolytic Disease of the Newborn (HDN).

Although this only happens in very rare cases, it is still something worth knowing about and worth discussing with your doctor if you think it may apply to you.

What can I do?

When you have a blood test at an ante-natal appointment, your doctor will assess yours and your partner's blood types. If you are rhesus negative and your partner rhesus positive, you may be given Anti-D injections which help to prevent antibodies being produced in your body and reacting against your baby. Though Anti-D can't get rid of antibodies if they're already in your system, it can stop them from forming in the first place - which is why it's important to identify this early.

Because of the Anti-D injection very few women develop antibodies nowadays, so it's rare that a baby with a different blood group to his or her mother is affected. However if your body does develop antibodies, your baby will be monitored closely for any signs of anaemia. In extreme cases your baby can be treated with a blood transfusion, ensuring he or she is born without complications.

In any case, when your baby is born his or her blood will be tested. If your baby is rhesus positive and you are rhesus negative you'll be given Anti-D injections so that any future pregnancies will not be affected by antibodies you may otherwise produce.

If you are concerned that your blood type may affect your pregnancy, it's always best to talk your concerns over with your GP, who will be able to give you professional advice.

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