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Blood tests

As part of your antenatal care you will be offered several blood tests. Some are offered to all women, and some may only be offered if you are at risk of a particular infection or inherited condition. All the tests are performed to make your pregnancy safer or to check that the baby is healthy. You don't have to have them if you don't want to. Talk to your midwife or doctor, and give yourself enough time to make your decision. They will also give you written information about the tests. Below is an outline of all the tests that can be offered.

Blood group

Your blood will be tested to see whether it is rhesus negative or positive. If you are rhesus negative, this isn't usually a concern for a first pregnancy, but it may affect the next baby if you get pregnant again.

People who are rhesus positive have a substance known as D antigen on the surface of their red blood cells. Rhesus negative people do not. A rhesus negative woman can carry a baby who is rhesus positive if the baby's father is rhesus positive. During the birth, the mother can produce antibodies against the baby if small amounts of the baby's blood enter her bloodstream. This usually does not affect the existing pregnancy, but the woman can become sensitised. This means that her immune response will be quicker and much greater if she gets pregnant with a rhesus positive baby again. The antibodies she produces can cross the placenta and may result in a condition called haemolytic disease of the newborn, which can lead to anaemia and jaundice in the baby.

Therefore, all women who are rhesus negative are offered a prophylactic Anti-D injection, between 28-30 weeks of pregnancy. Anti-D injections can reduce the risk of sensitisation. Following the birth of the baby, the rhesus factor of the baby is checked and if the baby is rhesus positive then the mother will be offered another injection of Anti-D.

If there are any incidents during the pregnancy which could result in fetal blood entering the mother’s circulation, then additional Anti-D may be offered at this time. This could include if any vaginal bleeding occurs or any abdominal trauma. In this situation please contact DAU or triage urgently.

Screening for Anaemia, Sickle Cell and Thalassaemia

All women are offered a blood test to find out if they anaemic. If the test shows that you are anaemic you will be recommended to take an iron supplement.

We also test for serious inherited blood disorders, which affect the haemoglobin. This is the part of the blood which carries oxygen around the body.  People who have these conditions will need specialist care. However, it is possible for some people to be ‘carriers’  and not be aware of their status, as they are fit and healthy and do not have the disorder. If a carrier was to have a baby with someone who is also a carrier then it is possible that their baby could inherit a disorder. Therefore, if a mum is a carrier, dad will be offered a test too.

Screening for Infections

You will be offered tests for:.

  • Syphilis. This is a sexually transmitted infection, which can be passed on through sexual contact or from mother to baby. This infection can lead to miscarriage and stillbirth and if left untreated may cause serious harm to the baby.
  • Hepatitis B. This is an infection caused by the hepatitis B virus, which can result in an acute and chronic infection. Hepatitis B is usually passed through infected blood and other body fluids. It too can be passed on from sexual contact and from mother to baby. All mothers found to be Hepatitis B positive are referred to a specialist team to ensure the most appropriate plan of care is in place. Babies born to mothers who are Hepatitis B positive will be offered a vaccination to reduce the risk of becoming infected.
  • HIV (human immunodeficiency virus). This retrovirus affects the immune system and leads to Acquired Immune Deficiency Syndrome (AIDS). HIV is passed on through sexual contact, infected blood and can be passed from mother to baby. All women are encouraged to have the HIV test. It is well evidenced that the risk of passing HIV onto the baby can be reduced from 25% to 1% with the right care and treatment. All women who are HIV positive are referred to a specialist team and confidentiality is maintained.

Please be aware that screening tests are only performed once in pregnancy. It is possible to acquire these infections at any stage in the pregnancy, therefore, if you or your partner feel you may be at risk during your pregnancy, please discuss this with your midwife. Please refer to the booklet ‘Screening tests for you and your Baby’ for more details.

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