Antenatal blood tests

You 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 yourself and your baby.

Whenever possible the taking of blood tests is timed so that you don’t need lots of needles on separate occasions!

Blood group

Usually at your booking appointment when you start your maternity care, your midwife or a nurse will take blood to find out which blood group you belong to (for example, O, A, B, AB). Knowing your blood group is important in case 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 factor

Your 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 or at birth, 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. In a future pregnancy if your baby is also rhesus positive the antibodies can 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.

Your blood can be checked during the pregnancy to ensure you have not already developed these antibodies and to protect future pregnacies you will be given injections called Anti-D which will stop your body producing antibodies. If you have an incident during pregnancy when some of your baby’s blood cells could have entered your circulation such as amniocnetesis or turning a breech baby (ECV) you may be given a further injection of Anti-D. After the birth a sample of the baby’s blood would be taken from the cord and if the baby is found to be Rhesus Positive another injection of Anti-D will be given to you.

Anaemia

You will be offered two tests to check for anaemia. If you become anaemic during pregnancy it will mean that you do not have enough to meet the needs of your baby in addition to your own requirements. If the results do show your iron levels are low you should be offered an iron supplement to take. Iron tablets can make you constipated so you may need to increase the roughage in your diet.

Rubella

Rubella is another name for German measles. If a woman catches rubella in pregnancy, it can cause miscarriage , stillbirth or her baby could have deafness, heart problems, brain damage and sight problems. 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 who could have rubella and to have the vaccination against rubella after having your baby.

Toxoplasmosis

Toxoplasmosis is a parasite infection found in cat faeces. It can be found in soil contaminated by cat faeces or in the meat of animals that have caught the parasite. You can avoid catching toxoplasmosis by:

• Ensuring all meat is thoroughly cooked so that it is no longer pink or blood visible and avoiding cured meats such as Parma Ham and salami
• Wash your hands, cooking utensils and surfaces after preparing raw meat
• Washing all soil from fruit and vegetables
•  Avoid changing cat litter trays or clearing cat faeces by asking someone to do this for you. If absolutely necessary wear glvoes and wash these and your hands thorughly afterwards.
• Wear gloves when gardening and do not touch your face with them
• Avoid drinking unpasteurised goat’s milk and products made from it.

Some people are already immune to the infection havin gpreviously had the infection at some time in their lives without noticing as it can have no symptoms or occasionally just mild-like flu symptoms. However, if you become infected with toxoplasmosis for the first time during pregnancy, your baby could be affected and runs the risk of problems such as eye damage or having learning difficulties or could be miscarried or stillborn. Women aren’t routinely tested for toxoplasmosis in the UK because only a few babies each year are severely affected by the parasite. If you think you have put yourself at risk of toxoplasmosis, ask your midwife if you can be tested. For more information contact Tommy’s the baby charity who have taken over the work of the Toxoplasmosis Trust.

Hepatitis B

Hepatitis B is a potentially serious infection which affects the liver. It  is usually transmitted by infected body fluids 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. Women are routinely tested for hepatitis B and if you are found to have had an infection, your baby will be offered vaccine treatment soon after birth to prevent liver disease.

HIV

All pregnant women in the UK are routinely offered a HIV test. Human immunodefiency virus (HIV) can be passed to the babies of infected mothers so it is important that women know their HIV status so that those affected can be treated during pregnancy, birth and post-natal period to reduce the risk of the baby becoming infected.

Sickle cell disease

Sickle cell disease is most common among people of Africa or Caribbean descent, although it also affects people from Asia, the Middle East or eastern Mediterranean. 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 of the affected gene, you have sickle cell trait which generally causes no problems but you can pass it on.

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 can block small blood vessels, causing severe pain. People with sickle cell disease can need regular blood transfusions throughout their lives.

If both you and your partner have sickle cell disease or sickle cell trait, your baby may 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:

•   25 per cent chance that your baby will not have sickle cell trait or sickle cell disease
•   50 per cent chance that your baby will have sickle cell trait
•   25 per cent chance that your baby will have sickle cell disease

Thalassaemia

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 be descendents of Mediterranean countries, the Middle East, Asia and Africa. 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 fibrosis

If 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 causes th einternal body secretions to become thick and sticky and this 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 often need physiotherapy and medication. Their life expectancy is often short, only about 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 to check whether your baby has cystic fibrosis.

Down’s syndrome

Combined, Double, triple, quadruple tests.In order to screen for Down’s syndrome, either ultrasound, blood tests or a combination of bothare used.

Between 11-14 weeks a nuchal scan and combined blood tests can be used to screen to see whether your baby is likely to have Down’s syndrome. By looking at both you are likely to have a more accurate result.

Between 15 – 20 weeks a double, triple or quadruple test can be used. The difference between these tests is the number of substances called markers that are looked for in your blood. Markers are indicators of the condition.

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). If your result is positive you are likely to be offered further diagnostic testing such as an amniocentesis or chorionic villus sampling (CVS).

Maternal age and risk of Down’s

When 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 have 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:

•   If you are outside the optimum testing time
•   If you are very overweight or very underweight
•   If you are Afro-Caribbean
•   If you are pregnant with twins
•   If you have diabetes which is controlled by insulin injections
•   If you have recently had any vaginal bleeding