Pregnancy Guide
NHS Choices

Screening for Down's Syndrome

What is Down’s syndrome?

Down’s syndrome is a genetic condition caused by an extra chromosome. A person with Down’s syndrome has 47 chromosomes instead of the usual 46.

People with Down’s syndrome are affected in different ways.  All have some learning disability. For some people this is mild, for others it is more severe. Most can lead nearly independent adult lives, but some need more support than others. Some also have medical conditions, such as heart problems. Many of these conditions can be treated.

What are my chances of having a baby with Down’s syndrome?

Down’s syndrome happens in about 1 in 450 pregnancies.  It does not usually run in families. All women have a chance of having a baby with Down’s syndrome. The chance increases with age but babies are also born with Down’s syndrome to younger women. This is why women of all ages are offered the screening test.

The result of the screening test will tell you your chance of having a baby with Down’s syndrome in this pregnancy.

What will the screening test result tell me?

There are a number of screening tests for Down’s syndrome. None of these tests show definitely whether a baby has Down’s syndrome or not. They only tell you what chance you have of your baby having Down’s syndrome.

The screening test does not pick up all babies affected by Down’s syndrome. On average, for every 10 babies with Down’s syndrome, only around seven or eight will be picked up by screening. This means two or three out of every 10 babies with Down’s syndrome will not be picked up by the screening test.

What are the advantages of having screening for Down’s syndrome?

If your baby has Down’s syndrome, you will be able to make choices about your pregnancy. For example, you can decide whether to prepare for the birth of a baby with Down’s syndrome or to end your pregnancy.

What are the disadvantages of having screening for Down’s syndrome?

Having the test may make you anxious especially if you have a result which shows you have a higher chance of having a baby with Down’s syndrome. Higher chance is how we describe your result if it is between 1 in 5 and 1 in 150.  If the result is between 1 in 5 and 1 in 150, you will be offered another test (procedure) to see if your baby definitely has Down’s syndrome. Because the procedure used can cause a miscarriage, many women find this a difficult decision. Some women may wish they had not had the screening test because making this decision is difficult. 

Should I have the test for Down’s syndrome?

Only you can decide whether to have the test or not. Some women want to find out if their baby has Down’s syndrome, and some don’t. All hospitals in Wales offer women a screening test for Down’s syndrome but the decision whether to have the test or not is yours. You can discuss with your midwife what you want to do. They will support you whatever you decide. 

What screening test will I be offered?

You will be offered an ultrasound scan (if possible, they will measure the small space at the back of the baby’s neck (nuchal translucency)). You will then be offered a blood test. The measurements taken at the scan, the results of the blood test and your age are used to work out the chance of your baby having Down’s syndrome. This test is taken when you are between 11 and 14 weeks pregnant.

Sometimes it is difficult to measure the nuchal translucency. For example, the baby may be lying in the wrong position or you may be above average weight for your height and this make looking at your baby difficult because the images are not clear. If the person performing the scan (the sonographer) cannot get a measurement, they will tell you. If they cannot get the measurement or if you go for the scan appointment later than 14 weeks pregnant, you can have a different blood test to find out your chance of having a baby with Down’s syndrome. This test is taken at 15 to 18 weeks of pregnancy.

You can choose whether or not to have an early pregnancy scan. You can also choose to have an early pregnancy scan but not to have the screening test for Down’s syndrome. 

You cannot have the Down’s syndrome screening test in this pregnancy if you are   carrying more than one baby.

The screening test is not usually offered after 18 weeks of pregnancy. If you are more than 18 weeks pregnant and would like to have Down’s syndrome screening, you will need to discuss this with your midwife or hospital doctor (obstetrician).  

Where can I have the test done?

Your midwife will tell you where the test can be done. 

Results

Will my results be confidential?

The NHS keeps the results of all tests confidential.  Hospital policies vary on how many health-care professionals have access to your test results.  Your midwife will be able to explain the local arrangements to you.

How will I get the result from my screening test?

Your midwife will tell you how and when you will get the result of the test. The results are given as either ‘higher chance’ or ‘low chance’.

What happens if I get a low chance result?

If the result shows you have a low chance of having a baby with Down’s syndrome, no more tests are offered. Please remember that having a low chance does not mean that you have no chance of having a baby with Down’s syndrome.

What if I have a higher chance result?

If your test result shows you have a higher chance of having a baby with Down’s syndrome (that is, a chance of 1 in 5 to 1 in 150), you will be offered an appointment with a midwife or doctor. They will explain your test result to you in detail, including your individual chance, and you can discuss whether or not you want to have a diagnostic procedure. You may face some difficult decisions after a diagnostic procedure that you need to be aware of beforehand.

Remember that the lower the number, the higher the chance.  So, for example, 1 in 80 is a higher chance of having a baby with Down’s syndrome than 1 in 400.

Between 2% and 4% of women (that is, between two and four out of 100) who have the screening test have a result which shows they have a higher chance of having a baby with Down’s syndrome.

The quality of the screening offered by the NHS in Wales is monitored. Some women pay privately to have Down’s syndrome screening.  Screening done by private clinics is not monitored by the NHS.  This means that your midwife will have no information about the quality and accuracy of any screening tests carried out by private clinics. 

Diagnostic procedure for Down’s syndrome

If you have a higher chance of having a baby with Down’s syndrome, you will be offered a diagnostic procedure.

This leaflet gives some basic information about the diagnostic procedures you could be offered if you have the screening test. More information is available in other leaflets and on our website.

What diagnostic procedures will I be offered?

Depending on how many weeks pregnant you are, you will be offered either a chorionic  villus sampling (CVS) or amniocentesis procedure.

What is chorionic villus sampling (CVS)

CVS is a procedure during which a doctor removes a small amount of tissue from your placenta (afterbirth) during your pregnancy. The cells in this tissue are tested in the laboratory to look at your baby’s chromosomes.

You can usually have CVS after you are 11 weeks pregnant. CVS involves some risk. It can cause a miscarriage in more than 1% but less than 2% of pregnancies.

What is amniocentesis?

An amniocentesis is a procedure to remove about 15 to 20 millilitres (that is, three to four teaspoons) of amniotic fluid from around the baby in the womb. The cells from your baby that are floating in this fluid can be tested in the laboratory to look at the chromosomes of the baby.

 It can be done after you are 15 weeks pregnant.

Amniocentesis involves some risk. It causes a miscarriage in around 1% of pregnancies (one in every 100 pregnancies). 

What would a diagnostic test result tell me?

The result would tell you if your baby has Down’s syndrome. If the baby has Down’s syndrome, you can decide whether to prepare for the birth of a baby with Down’s syndrome or to end your pregnancy.

These tests can detect other chromosome abnormalities as well as Down’s syndrome and if you are offered a chorionic villus sampling (CVS) or an amniocentesis, this will be explained to you.

More information

You can get information about Down’s syndrome screening from your midwife or your hospital doctor (your obstetrician) or from www.antenatalscreening.wales.nhs.uk

Antenatal Results and Choices (ARC)

345 City Road
London
EC1V 1LR

Helpline: 0845 077 2290
E-mail: info@arc-uk.org
Website: www.arc-uk.org

Down’s Syndrome Association (DSA)

Langdon Down Centre
2a Langdon Park
Teddington
TW11 9PS
Phone: 0222 1212 300
Fax: 0845 230 0373
E-mail: info@downs-syndrome.org.uk
Website: www.downs-syndrome.org.uk

 


Last Updated: 08/11/2017 13:27:16