pregnant women getting a blood test
Louise Broadbridge
Louise Broadbridge

What does it mean to be rhesus negative?

At your first appointment with your midwife, you will provide samples of your blood for testing. From this, you will find out what your blood group is and whether you are rhesus positive or negative.

Around one in six women in the UK are rhesus negative, which means their blood does not have the rhesus (Rh) antigen which is found on the surface of blood cells.. If you are rhesus negative, you blood type will be followed by a negative symbol like O-, A-, B- or AB-. 

Being rhesus negative is not usually a problem and you probably won’t even know your blood type unless you have been pregnant before or you have been a blood donor. However, if you are pregnant, there is a risk of developing rhesus disease if your baby is rhesus positive.

What is rhesus disease?

Rhesus disease is when the antibodies in an expectant mother’s blood attack her baby’s blood cells. The mother is not affected by this but it can cause problems for the baby and they can become anaemic as their red blood cells are being destroyed by their mother’s antibodies.

Rhesus disease makes a baby more likely to develop newborn jaundice, where their skin turns yellow. Jaundice happens when babies have too much bilirubin, a pigment made from the breakdown of red blood cells.

Rhesus disease only happens when a baby with rhesus positive blood is being carried by a mother who is rhesus negative. The risk is higher when the mother has been pregnant before or been previously exposed to rhesus positive blood.

This exposure causes her blood to produce antibodies, which fight against the rhesus positive blood cells and destroy them. During pregnancy, these antibodies can cross the placenta and affect the baby. Rhesus disease can also continue having an impact for the first few months after they are born.

What will happen if I am rhesus negative?

If you are rhesus negative, your midwife will talk to you about what this means. You will be offered a treatment called anti-D injections during your pregnancy to reduce the risk of your baby developing rhesus disease. 

These injections contain anti-D immunoglobulin, a concentrated antibody preparation which is made from plasma collected from blood donors. This will neutralise any rhesus positive antigens which may have entered your bloodstream so your body will not produce antibodies which could harm your baby.

If you have already developed anti-D antibodies during a previous pregnancy, for example, if you didn’t receive the anti-D injections, your pregnancy will need to be closely monitored. Additional checks will also need to be made on your baby after birth. 

You may be given two doses of anti-D injections, the first during the 28th week of pregnancy and the second during the 34th week. Alternatively, you may be given a single dose between weeks 28 and 30. Whether you are given a single or double dose will depend on your hospital trust but both are equally effective. 

Once your baby is born, a blood sample will be taken from their umbilical cord. If they are found to be rhesus positive, you will be given an additional anti-D injection within 72 hours of the birth. This will destroy any rhesus positive blood cells which may have entered your bloodstream during the delivery.

If anything happens in your pregnancy which is thought to increase the risk of your baby’s blood entering yours, you will be offered an anti-D injection. For example, you may be given an additional injection if you experience bleeding, injure your abdomen or have an invasive test like an amniocentesis.

Do I have to have anti-D injections?

All medical procedures require your consent and you can refuse to have anti-D injections during your pregnancy. However, this will increase the risk of your baby or future babies developing rhesus disease.

If your baby does get rhesus disease, they may need extra care after they are born. This could include phototherapy, where they are placed under lights, an injection of intravenous immunoglobulin to protect their red blood cells or they may even need a blood transfusion.

Babies with rhesus disease are likely to need to spend time in the neonatal unit and they will need additional care and monitoring. If it is left untreated, it can cause serious problems including sight loss, hearing loss, brain damage and learning difficulties.

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