Blood testsYou will be offered a variety of blood tests during your pregnancy. By testing your blood, a great deal can be deduced about the likely health of your baby.Most of the tests described here can be carried out on a single sample of blood so you won’t have to give a separate sample for each test! Blood group When you go to book for maternity care at your local surgery, your midwife or GP will take blood to find out which blood group you belong to (for example, O, A, AB). Then, if by chance you lose a lot of blood when you give birth, it will be possible to give you a transfusion which matches your own blood. Rhesus factorYour blood will also be tested to see whether you are Rhesus positive (which means that you do have Rhesus factor) or Rhesus negative (which means that you don’t). Rhesus factor isn’t a problem unless you are negative and your baby is positive. In this situation, if a few of your baby’s blood cells get into your circulation during pregnancy, your body will recognise that they have something which your own blood cells haven’t (ie, the Rhesus factor). Your body will then treat your baby’s red blood cells as invaders and manufacture antibodies to destroy them. The antibodies cross the placenta and start to destroy the blood cells in your baby’s circulation. All this won’t have time to happen in your first pregnancy but your body will react next time you are pregnant with a baby who is Rhesus positive. Because you can never be absolutely certain that this is your first pregnancy (you could have had a previous pregnancy which miscarried before you were even aware of it), your doctor will arrange for you to have injections if you are Rhesus negative to ensure that your baby is kept safe. The doctor won’t try to find out what your baby’s blood group actually is, she will simply treat you as if your baby was definitely known to be Rhesus positive. RubellaRubella is another name for German measles. If a woman catches rubella for the first time in early pregnancy, her baby runs a very high risk of being born blind or deaf, and of having heart problems and learning difficulties. If your blood test shows that you are immune to rubella, there’s nothing to worry about. If you are not immune, you will be advised to keep well away from anyone, and especially a child, who could have rubella. If your blood shows that you have recently been infected with rubella (and remember that the disease can be very mild so you may not even have felt particularly unwell), you may be offered a termination of pregnancy because your baby is very likely to be damaged. You shouldn’t be put under any pressure to agree to this - it’s your decision. ToxoplasmosisToxoplasmosis is a parasite infection which you can catch by:
Many people have had the infection at some time in their lives without even noticing its mild flu-like symptoms and are now immune from the disease. However, if you become infected with toxoplasmosis for the first time during your pregnancy, your baby could be affected and runs the risk of eye damage or having learning difficulties. Women aren’t routinely tested for toxoplasmosis in the UK because only about 50-60 babies a year are severely affected by the parasite. If you are really worried about toxoplasmosis, ask your doctor if you can be tested. Be aware that one test probably won’t be enough and you may have to provide more blood samples to be sent to a Toxoplasma Referral Centre.For more information contact the Toxoplasmosis Trust*. Hepatitis BHepatitis B is usually transmitted by infected blood and you can be a carrier without having any symptoms. The later it is contracted in pregnancy, the higher the risk of passing it on to the child, who may then become a carrier. Most antenatal clinics test women routinely for hepatitis B and if you are found to have had a recent infection, your baby will be offered vaccine treatment soon after birth to prevent liver disease. HIVSome clinics screen women anonymously for HIV. This means that your blood is put into an unnamed tube so that nobody knows that it has come from you. Anonymous testing is carried out simply to get an idea of how the disease is spreading through the community. You might decide that you want to have a named test for HIV because you have or have had a partner whom you know or suspect is positive, or because you have shared needles for injecting drugs. The advantages of knowing your HIV status are:
There are also some disadvantages to consider:
These are very real fears, but remember that health professionals are just as concerned about patient confidentiality as you are, and Social Services don’t take babies away from their mothers simply because the mothers are HIV positive. Unless you are very ill indeed, you are always considered to be the best mother for your baby. Before you decide whether or not to have an HIV test, ask to talk to your doctor or your midwife. There may be a midwife at the hospital with specialist knowledge of HIV who is trained in counselling. If you can’t find a sympathetic or knowledgeable health professional, contact Positively Women. Sickle cell diseaseSickle cell disease is most common among people from West Africa, the Caribbean, the Middle East or India. However, it’s certainly not exclusive to these parts of the world. You have to have received sickle cell genes from both your parents in order to have sickle cell disease. If you have received only one gene, you have sickle cell trait which generally causes no problems. Sickle cell disease is the result of the bone marrow producing blood cells which are crescent or sickle shaped rather than spherical. These abnormal cells are broken down by the body very quickly, giving rise to anaemia. They also tend to block small blood vessels, causing severe pain. People with sickle cell disease need regular blood transfusions throughout their lives. If both you and your partner have sickle cell disease, your baby will also be born with the disease and, before starting a pregnancy, you should ask your GP to refer you to a genetic counsellor. If you have sickle cell trait, you might want your partner’s blood to be tested because if only one of you has the trait, your baby will not have sickle cell disease (although he or she might have sickle cell trait). If you both have the trait, the risk to your baby is as follows:
Thalassaemia is another blood disorder that is caused by abnormal genes. The pattern of inheritance is exactly the same as for sickle cell so your baby needs to have received an abnormal gene from both you and your partner for him to have full blown thalassaemia. If he only has one abnormal gene, he will have thalassaemia trait which is much less severe. People who carry thalassaemia genes are most likely to come from Mediterranean countries, the Middle East or South-East Asia. You and your partner might both want to be tested to see whether you are carriers for thalassaemia and make further decisions about antenatal tests based on the results of you own blood tests. Cystic fibrosisIf you come from a family where someone has cystic fibrosis you are likely to be anxious that your baby might also be affected. Many white people are carriers of the cystic fibrosis gene (1 in 25); it’s much less common to be a cystic fibrosis carrier if you come from other racial groups. Just as with sickle cell and thalassaemia, a baby will only be affected if he receives abnormal genes from both his parents. Cystic fibrosis affects the baby’s lungs and digestive system. The lungs become clogged with thick secretions, and the juices which normally help to digest food don’t flow properly through the digestive tract. As they grow up, children who have cystic fibrosis need daily physiotherapy and medication. Their life expectancy is often short, only about 20 to 30 years. You and your partner can find out if you are carriers of cystic fibrosis by having a mouth wash test which your GP should be able to arrange for you. (You may have to pay for the test if there is no family history of cystic fibrosis that puts you at increased risk.) The mouth wash test is a screening test and it only tells you whether it is likely or unlikely that you are a carrier of cystic fibrosis. If you are both high risk, you might want to have chorionic villus sampling or amniocentesis to check whether your baby has cystic fibrosis. Note: The cystic fibrosis gene takes many different forms and the mouth wash test only screens for some of them. So you and your partner could be told that the test shows you are at low risk of being carriers, and yet you could still have a baby with cystic fibrosis. Down’s syndrome and spina bifidaAlphafeto protein (AFP)Measuring the amount of alphafeto protein (AFP) in your blood is the simplest way of screening for spina bifida. If the level of AFP in your blood is very high, this could indicate that your baby has spina bifida or anencephaly. Double, triple, quadruple testsIn order to screen for Down’s syndrome, both AFP and some other markers will be measured. Markers are substances in your blood which can give information about whether your baby is likely to have Down’s syndrome. If your blood is only tested for one marker (this would be AFP), the results are less accurate than if your blood is tested for two markers (double test) or three (triple test). A fourth marker (quadruple test) will only be used if, for some reason, you are thought to be at very high risk of having a baby with Down’s syndrome. To be screened for spina bifida and Down’s syndrome, you need to give a sample of blood when you are 16 to 18 weeks pregnant. It’s vital that you aren’t more or less pregnant than this, otherwise the test results will be inaccurate. The results will tell you whether you are screen negative (ie, your risk of having an affected baby is less than 1 in 250) or screen positive (ie, your risk is more than 1 in 250). Maternal age and risk of Down’sWhen your blood is tested for Down’s syndrome, your age will also be taken into account. The older you are, the more likely you are to conceive a baby with Down’s.
It could be that your age will skew the results of your blood test. For example, if you are 40, even though your blood test shows a low risk of Down’s, you might well come out as screen positive when your age-related risk is added in. Always remember that screening tests are not very reliable. There are a number of factors which could influence their accuracy. For example:
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