Choosing whether to have the tests is an important decision, for you and for your baby.

This chapter gives you some information about Down's syndrome and about testing for it, so you can decide whether to have the tests.

Pregnant women are offered tests for Down's syndrome. This booklet gives you some information about Down's syndrome and about testing for it, so you can decide whether to have the tests.

Choosing whether to have the tests is an important decision, for you and for your baby. You need to make the decision that is right for you, so please read this booklet carefully.

Your obstetrician or nurse will talk to you about testing for Down's syndrome. They will be happy to answer your questions – so please do ask if there is anything you are not clear about.

There is no such thing as a typical person with Down's syndrome. Like all people, they vary a lot in appearance, personality and ability. People with Down's syndrome have learning difficulties. Some have more serious difficulties than others.

It is hard to tell in babies how much they will be affected as children, or when they are grown up. Some adults with Down's syndrome are able to get jobs and live fairly independent lives. However, most people with Down's syndrome need long-term help and support. A number of health problems are linked to Down's syndrome. But again, people vary, and some people with Down's syndrome enjoy good health. Problems which are linked with Down's syndrome include heart problems and reduced hearing and vision. Many of the problems can be treated, and frequent health checks can make sure that any problems are picked up as early as possible. Most people with Down's syndrome live to be 50 years of age and some live to be over 70. Alzheimer's disease (a form of senile dementia) may affect people with Down's syndrome at an earlier age than other people.

People do not usually expect to have a baby with Down's syndrome. It does not usually run in families. Some people think that only older women can have a baby with Down's syndrome, but this is not true. Anyone can have a baby with Down's syndrome, but the risk does go up with age. The older a mother is the more chance she has of having a baby with the condition. For example, the chance of having a baby with Down's syndrome is one in 1500 for women who are 20 years old, one in 900 for women who are 30 years old, and one in I00 for women who are 40 years old. Some people prefer to think of the risk as a percentage. A risk of one in 1500 is the same as a 0.07% risk. A risk of one in 900 is the same as a 0.1% risk. A risk of one in I00 is the same as an l% risk.

Inside all the cells of our bodies are tiny structures called chromosomes. These chromosomes carry the genes that determine how we develop. Most people have 23 pairs of chromosomes in each of their cells. When our bodies produce the special cells needed to make babies, the chromosome pairs divide and rearrange themselves.
Sometimes these pairs of chromosomes do not divide correctly, and this causes the baby's cells to have an extra copy of chromosome number 2l. This causes Down's syndrome. (And it is the reason why one of the medical names for Down's syndrome is Trisomy 21.) The extra chromosome cannot be removed from cells, so there is no cure for the condition. If the chromosomes divide incorrectly, this happens by accident. It is not caused by anything parents have done or have not done.

Should l have the tests for Down's syndrome? Only you can decide that. Some women want to find out if their baby has Down's syndrome, and some do not. Information about the tests and how they work can help you make up your mind. This booklet gives the main facts.

We do not offer all women a test that will tell them for certain. This section explains why. There are tests which give definite information. These are called diagnostic tests. The problem is that having a diagnostic test increases the risk of miscarriage. This is why we do not offer diagnostic tests to all women. Instead, we offer tests in two stages. We begin by offering all women a test that carries no risk of miscarriage. This type of test is called a screening test. Screening tests do not give a definite answer, but they do tell us which babies have an increased risk of having Down's syndrome. We then offer diagnostic tests to the women at increased risk. (There is more information on diagnostic tests later in the booklet.) If your screening result shows that you are at higher risk then you will be offered a diagnostic test. It is very important to understand that screening tests cannot tell you that your baby definitely does or definitely does not have Down's syndrome. We only use screening tests, and the two-stage process, because we do not have a risk-free diagnostic test to offer. You can choose whether or not to have both parts of the testing process. If you decide to have a screening test, and we later offer you a diagnostic test, it is your choice whether or not to have that test. We explain more about the two-stage process later in the leaflet.

All the tests described later give results in the form of, "one in ...", for example, "one in 100" or "one in 1500". (The same results can also be given as percentages.) These numbers tell us how likely it is that the baby has Down's syndrome. For example, the result "one in 100" means that there is one chance in 100 that the baby has Down's syndrome. The result "one in 1500" means that there is one chance in 1500 that the baby has the condition. It is very important to understand that as the second number in the result gets bigger, Down's syndrome gets less likely. Next we explain how we use the results from the screening test to decide whether to offer you more tests.

If the screening test shows the risk of the baby having Down's syndrome is lower than the recommended national cut off, we will not offer you a diagnostic test. Most screening test results (about 95%) fall into this category. This is known as having a "low risk" result. It is important to understand that a low-risk result means exactly that. It does not mean that there is no risk at all that the baby has Down's syndrome, just that it is unlikely. It means that the measured chance is lower than the one for offering more tests. There is still a small risk because some babies with Down's syndrome are not detected by screening tests. This happens if the expected pattern is not seen in the blood test or scan measurements, because of natural differences. Overall, about a quarter of babies with Down's syndrome are not detected by screening tests.

If the result of the screening test shows the risk of the baby having Down's syndrome is greater than the recommended national cut off we will offer you a diagnostic test. The screening results that lead to us offering you more tests are sometimes, known as "increased-risk" results. Overall about one in 30 (3%) women screened has a "increased-risk" result and are offered a diagnostic test. It is very important to remember how screening tests fit into the two-stage process. If you get a high-risk result from a screening test, it means that we will offer you more tests. It does not mean that the baby definitely has Down's syndrome. As we explain later, most of the women who are offered further tests learn that their baby does not have Down's syndrome.

There are several different ways of screening for Down's syndrome. In the past, screening was just based on a woman's age, and we offered diagnostic tests to all women over a certain age. Today's screening tests can provide women of all ages with information about the chance of their baby having Down's syndrome. These tests use blood samples taken from the mother, special ultrasound scans, or both. In this section we describe the most common tests we use at the moment. Different maternity units may use different tests.

Blood tests measure the amount of some substances that are found naturally in the mother's blood. These substances have passed to the mother from the baby. A sample of the mother's blood is usually taken between 10 to 18 weeks. The timing of the test and details of the substances measured may vary slightly between different maternity units.

A "nuchal translucency scan" (NT) is a special ultrasound scan which is done at 11 to 13 weeks. The amount of fluid lying under the skin at the back of the baby's neck is measured.

We can combine the result of the nuchal translucency ultrasound scan and a blood test taken from the mother to work out a risk figure.

Your doctor will discuss the results with you and answer any questions that you have. You will be offered a diagnostic test which would tell you definitely whether your baby has Down's syndrome or not. There are two diagnostic tests available - chorionic villus sampling (CVS) is performed from 11 to 14 weeks, and amniocentesis is performed from 16 weeks of pregnancy. If you do get a high-risk result from a screening test, your midwife or doctor will give you information and support. You will also have time to make up your mind about what to do next.

If you are in this position it is important to understand that you have a difficult decision to make. You have two options. You can decide not to have a diagnostic test. This means spending the rest of your pregnancy knowing the screening result, which might be stressful. The only other option is to have the diagnostic test, knowing that this will slightly increase the risk of miscarriage. You need to think carefully about what you would do if you found yourself in this position. Once you know the result of the screening test, you can't put the clock back. If you would not be happy with either of the above options, you need to consider very carefully whether it would be better for you not to have the screening tests in the first place.

At the time of your test, ask your doctor how you will get the results. The test results should be available within two weeks.

Although your risk is low, you may want to discuss your results with your doctor.

This leaflet just gives some basic facts to help you decide whether you want to have any screening or diagnostic tests you are offered. If you are actually facing a decision about diagnostic testing, your doctor will give you more detailed information.

Amniocentesis can be done from 16 weeks of pregnancy. It is a widely used procedure which usually takes about 10 minutes. You will have an ultrasound scan to check the position of the baby in the womb. A fine needle will then be inserted through your abdomen into the womb. A sample of fluid surrounding the baby (amniotic fluid) will be taken. This fluid contains cells from the baby, which will be examined at the laboratory and the baby's chromosomes will be counted. About one in every 100 samples does not produce a result because the cells do not grow, or the results are not clear. If this happens, you will be offered a second amniocentesis.

CVS can be done from 11 weeks of pregnancy. It is usually only offered in a specialist centre. An ultrasound scan is used to guide a fine needle either through your vagina or through your abdomen. A small sample of tissue is taken from the placenta. The sample is analysed in the laboratory, and the baby's chromosomes are counted. As with amniocentesis, very occasionally, about two in every 100 CVS samples do not produce a result.

These procedures are not completely safe, and this is why we don't offer them to everybody. For every 100 women who have amniocentesis, one will miscarry. And for every 100 women who have CVS, one or two will miscarry. These figures vary slightly from hospital to hospital. If you would like to know the miscarriage rates after CVS or amniocentesis in your hospital, please ask your doctor.

Many women find the procedures uncomfortable but they should not be painful. For a day or two afterwards, you will be advised to take things easy. If possible, you should avoid activities that involve lifting, bending or stretching. You may have some discomfort in your lower abdomen for a day or two after the procedure. This is normal, and you can take paracetamol to relieve the discomfort.

It can take up to 18 days to get the results of diagnostic tests. Some hospitals offer "molecular" tests as part of the diagnostic test. These are usually known by their initials - FISH and PCR. These tests provide some information within two to three days. Waiting for the results can be an anxious time.

It is important that you talk to your doctor about how you want to receive the results. The chances are that testing for Down's syndrome your results will show that your baby does not have Down's syndrome, but if the results show that your baby does have Down's syndrome, you need to think carefully about how you want to hear this information. Your doctor can give you the results at the antenatal clinic or in a letter. Discuss what is appropriate for you with your doctor.

The baby does not have Down's syndrome. This is the result that most women get. Some women are happy just to get this news. They do not want to talk about tests and test results any more. Other women want to discuss the results with somebody. They want to know how the two tests they have had - the screening test and the diagnostic test - can seem to say different things. If you really don't want to read any more details, just remember, the diagnostic test gives the definite result. We explained earlier that we use screening tests to decide who should be offered a diagnostic test. What the screening tests do is tell us if there is a certain sort of pattern in your blood-test or ultrasound results. This pattern is one that can sometimes be seen when a baby has Down's syndrome. The problem is that the same pattern can also be seen in many normal pregnancies. People's blood-test and scan results vary for all sorts of normal reasons. Screening tests just detect the pattern; they don't tell us the reason for the pattern. Only diagnostic tests can tell us if the reason for the pattern is that the baby has Down's syndrome. When a woman has a diagnostic test and the result shows her baby does not have Down's syndrome, that woman's earlier screening test result is sometimes called a "false positive" result. If this happens and you feel confused or upset about it, please talk to your doctor.

The main purpose of an amniocentesis or CVS is to find out whether a baby has Down's syndrome. But when the baby's chromosomes are examined, very occasionally other chromosome variations are identified. Some of these chromosome variations can be serious, and others will have only a minor effect, or no effect, on the baby. If the tests show there is a problem, you will be referred to a genetic counsellor for specialist information and support.

A small number of women who have a diagnostic test will learn that their baby has Down's syndrome. They then have three options, and it is entirely the parents' decision which they choose. Some people will decide to continue with the pregnancy, make plans and prepare for any extra challenges they might face bringing up a child with Down's syndrome. Some people may feel unable to bring up their child themselves, and decide on adoption. Other people will decide they do not want to continue with the pregnancy, and will choose to have a termination.

If you are faced with this decision, you need to make sure you reach the right decision for you. We will give you information and support to help you make your decision, but it is up to you to decide what will be best for you. You will have the opportunity to discuss your options with healthcare professionals, and you will also be offered information and support from outside the health service. You will have time to decide what you are going to do and your GP and midwife will support you in your decision.