Pregnancy and baby

Screening for Down's, Edwards' and Patau's syndromes

What is the test for Down syndrome?

Media last reviewed: 17/03/2014

Next review due: 17/03/2016

Screening for Down's, Edwards' and Patau's syndromes

All pregnant women are offered screening for Down's syndrome, as well as tests for Edwards' and Patau's syndromes. This is to assess your chance of having a baby with these conditions.

Down's syndrome is also called Trisomy 21 or T21. Edwards' syndrome is also called Trisomy 18 or T18, and Patau's syndrome is also called Trisomy 13 or T13.

The screening tests are:

  • a blood test plus nuchal translucency ultrasound scan (nuchal translucency is a collection of fluid at the back of the baby's neck) – this is called the combined test, and is offered between 11 and 14 weeks of pregnancy

    or
  • a blood test that can be offered between 14 and 20 weeks of pregnancy if you are too far along to have the combined test – this blood test is less accurate than the combined test

If these screening tests show that you have a risk greater than 1 in 150 (that is, between 1 in 2 and 1 in 150) of having a baby with Down's, Edwards' or Patau's syndromes, you will be offered diagnostic tests to find out for certain if your baby has the condition. The diagnostic tests are: 

  • chorionic villus sampling (CVS)
    or
  • amniocentesis

What are Down's, Edwards' and Patau's syndromes?

Inside the cells of our bodies there are tiny structures called chromosomes. Chromosomes carry the genes that determine how we develop. There are 23 pairs of chromosomes in each cell.

Problems can occur when sperm or egg cells are produced, which can lead to a baby having an extra chromosome. 

Find out more about chromosomes.

Down's syndrome

In Down's syndrome there is an extra copy of chromosome 21 in each cell. A baby born with Down's syndrome will have a learning disability. This means they will find it harder than most people to understand and learn new things. They may have communication problems and difficulty managing some everyday tasks.

It is impossible to know what level of learning disability a baby with Down's syndrome will have. It can vary from mild to severe. Most children with Down's syndrome attend mainstream primary school.

People with Down's syndrome can have a good quality of life. With support from their family and others, many people are able to get jobs and live fairly independently.

Some health problems are more common in people with Down's syndrome, such as heart conditions and problems with the digestive system, hearing and vision. Sometimes these problems can be serious, but many can be treated. With good healthcare, someone with Down's syndrome can live to around 60 years.

People with Down's syndrome have almond-shaped eyes and distinctive facial features, but they do not all look the same. Like all children, they also inherit features from their parents.

Read more about Down's syndrome.

What causes Down's syndrome?

Down's syndrome is not usually an inherited condition. In most cases it happens by chance. There are rare occasions when some extra chromosome 21 material can be passed on. This is called translocation.

Women of any age can have a baby with Down's syndrome, although the chance of having a baby with the condition increases with age. The older a woman is, the more likely she is to have a baby with Down's syndrome:

  • a 20-year-old woman has a 1 in 1,500 chance of having a pregnancy affected by Down's syndrome (this is a probability of 0.07%)
  • a 30-year-old woman has a 1 in 900 chance of having a pregnancy affected by Down's syndrome (a probability of 0.1%)
  • a 40-year-old woman has a 1 in 100 chance of having a baby affected by Down's syndrome (a probability of 1%)

These are background risks based on the woman's age alone. The combined screening test may give you a higher or lower risk than this.

Edwards' and Patau's syndromes

In Edwards' syndrome there is an extra copy of chromosome 18 in each cell. In Patau's syndrome there is an extra copy of chromosome 13 in each cell.

Sadly, most babies with Edwards' or Patau's syndromes will die before they are born or die shortly after birth. Some babies may survive to adulthood, but this is rare.

All babies born with Edwards' or Patau's syndromes will have a wide range of problems, which are usually very serious. These may include major brain abnormalities.

Babies affected by Edwards' syndrome can have heart problems, unusual head and facial features, growth problems, and be unable to stand or walk. Edwards' syndrome affects about 3 out of every 10,000 births.

Babies affected by Patau's syndrome can have heart problems, a cleft lip and palate, growth problems, poorly formed eyes and ears, problems with their kidneys, and be unable to stand or walk. Patau's syndrome affects about 2 out of every 10,000 births.

Find out more about Edwards' syndrome and Patau's syndrome.

What causes Edwards' or Patau's syndromes?

Anyone can have a baby with Edwards' or Patau's syndromes. In most cases these conditions do not run in the family. It is not the result of anything you did or did not do. The chance of having a baby with Edwards' or Patau's syndromes increases with age, so older mothers will have a higher chance of having a baby with these conditions.

What does the screening test involve?

A screening test for Down's, Edwards' and Patau's syndromes is available between 10 and 14 weeks of pregnancy. It is called the combined test because it combines an ultrasound scan with a blood test. The scan can be carried out at the same time as the dating scan.

If you choose to have the test, a blood sample will be taken from you. At the dating ultrasound scan, the fluid at the back of the baby's neck is measured (known as the nuchal translucency). The information from these two tests is used to work out the risk of the baby having Down's syndrome, or Edwards' or Patau's syndromes.

It is not always possible to obtain this measurement, and depends on the position of the baby. If this is the case, you will be offered a different blood screening test between 14 and 20 weeks.

If you are too far on in your pregnancy (more than 14 weeks) to have the combined test, you will be offered the blood screening test between 14 and 20 weeks of pregnancy. This test is not quite as accurate as the combined test.

If you are too far on in your pregnancy to have the combined test for Edwards' and Patau's syndromes, you will be offered a mid-pregnancy scan, which will look for physical abnormalities.

Can this screening test harm me or my baby?

The screening test cannot harm you or the baby, but it is important to consider whether to have this test carefully. This test cannot tell you for certain if the baby has Down's, Edward's or Patau's syndromes or not.

The test can provide information that may lead to further important decisions. For example, you may be offered diagnostic tests that can tell you for certain whether the baby has these conditions, but these tests have a risk of miscarriage.

Do I need to have screening for Down's, Edwards' or Patau's syndromes?

You do not need to have this screening test – it is your choice whether or not to have it. Some people want to find out the risk of their baby having these conditions, and some do not.

You can choose to have screening for:

  • all the conditions (Down's, Edwards' and Patau's syndromes)
  • Down's syndrome only
  • Edwards' and Patau's syndromes only
  • none of the conditions

What if I decide not to have this test?

If you choose not to have the screening test for Down's, Edwards' or Patau's syndromes, you can still choose to have other tests.

If you choose not to have the screening test for these conditions, it is important to understand that if you have a scan at any point during your pregnancy, it could pick up physical abnormalities.

These could be related to Down's, Edwards' or Patau's syndromes, but there is a chance that other problems could be picked up on a scan. The person scanning you will always tell you if any abnormalities are found.

Getting your results

The screening test will not tell you if your baby has Down's, Edwards' or Patau's syndromes or not. It will tell you if you have a higher or lower risk of having a baby with one of these conditions.

If you have screening for all three syndromes, you will receive one risk for Down's syndrome and one combined risk for Edwards' and Patau's syndromes (two risks altogether).

If your screening test shows a lower-risk result, you should be told within two weeks of the test being taken. If your screening test shows a higher-risk result, you should be told within three working days of the blood test result being available.

This may take a little longer if your test is sent to another hospital. It may be worth asking the midwife what happens in your area and when you can expect to get your results. You will be offered an appointment to discuss the test results and the further options you will have.

The charity Antenatal Results and Choices (ARC) offers lots of information about screening results and the options you face if you get a higher-risk result. There is also an ARC forum, where you can be put in touch with people who are in the same situation as you. You can read about people's experiences of making their decisions on the ARC website.

Possible results

If the screening test shows that the chance of having a baby with Down's or Edwards' and Patau's syndromes is lower than 1 in 150, this is a lower-risk result. More than 95 out of 100 screening test results (95%) will be lower risk. A lower-risk result does not mean there is no risk at all of the baby having Down's, Edwards' or Patau's syndromes.

If the screening test shows that the chance of the baby having Down's, Edwards' or Patau's syndromes is higher than 1 in 150 (that is, between 1 in 2 and 1 in 150), this is called a higher-risk result.

Fewer than 1 in 20 test results (5%) will be higher risk. This means that of 100 women accepting screening for Down's, Edwards' and Patau's syndromes, fewer than five will have a higher-risk result. A higher-risk result does not mean the baby definitely has Down's, Edwards' or Patau's syndromes.

Will I need further tests?

If you have a lower-risk result, you will not be offered a further test. If you have a higher-risk result, you will be offered a diagnostic test, such as amniocentesis or CVS. This will tell you for certain whether the baby has Down's, Edwards' or Patau's syndrome or not.

About 1 in 100 diagnostic tests (1%) result in a miscarriage. It is up to you whether or not to have the further tests. When trying to decide whether to have a diagnostic test, try to balance up the risk of miscarriage with how important the result will be to you.

Chorionic villus sampling (CVS)

This diagnostic test is usually done between 11 and 14 weeks of pregnancy. A fine needle, usually put through the mother's abdomen, is used to take a tiny sample of tissue from the placenta. The cells from the tissue are then tested for Down's, Edwards' or Patau's syndromes.

Read more about CVS.

Amniocentesis

Amniocentesis is done from around week 15 of pregnancy. A fine needle is passed through the mother's abdomen into the uterus to collect a small sample of the fluid surrounding the baby. The fluid contains cells from the baby, which are tested for Down's, Edwards' or Patau's syndromes.

Read more about amniocentesis.

If you find out your unborn baby has Down's, Edwards' or Patau's syndrome

A small number of women who have a diagnostic test will find out their baby has Down's, Edwards' or Patau's syndrome. They then have two options.

Some women decide to continue with the pregnancy and prepare for their child with the condition; others decide they do not want to continue with the pregnancy and have a termination (abortion).

If you are faced with this choice, you will get support from health professionals to help you make your decision. Support for parents is also available from the charity Antenatal Results and Choices (ARC).

The Down's Syndrome Association also has useful information on screening, and the UK National Screening Committee has produced a booklet called Screening tests for you and your baby.

The charity SOFT UK offers information and support through diagnosis, bereavement, pregnancy decisions and caring for all UK families affected by Edwards' syndrome (T18) or Patau's syndrome (T13). 

Page last reviewed: 09/02/2015

Next review due: 09/02/2017

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Comments

The 4 comments posted are personal views. Any information they give has not been checked and may not be accurate.

stephrob said on 20 June 2014

Hi,

My husband and I have decided we do not want to have any screening for Down's Syndrome, and just wondered do I need to let the hospital know before I arrive for my scan?

Thanks

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Kathryn at NHS Choices said on 01 July 2013

Dear agnesandzoe,

I asked the DH screening team about this and here is their response:

`A combined screen in the first trimester can be offered to women having twins – that would constitute a nuchal translucency scan plus biochemistry and this is clear in the standards.

The standards are currently under review and the issue of offering serum screening alone in the second trimester is being investigated but there has been no policy change as yet so the current position with second trimester serum screening is that it is not recommend for use in women with multiple pregnancies'.

Hope that clarifies the issue for you.
All best,
Kathryn Bingham, editor at NHS Choices

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agnesandzoe said on 15 January 2013

Hi there,
Please could you confirm that the information above, that "Serum screening is not used for pregnancies of twins, triplets or more", is up to date.
My midwife at Manchester St. Mary hospital advised it was out of date and that in fact serum testing is used in twin pregnancy, the values get divided equally between the two babies.
Thanks.

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agnesandzoe said on 15 January 2013

I just spoke to a midwife in St Mary hospital in Manchester. She told me that contrary to the info on this website serum screening IS used for down syndrome screening even in the case of twins.
She advised the info on your website which states serum is not used is probably out of date. Please could you respond to reassure me what info is correct?

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