Guidance

Down’s syndrome, Edwards’ syndrome and Patau’s syndrome

Updated 3 July 2024

Public Health England (PHE) created this information on behalf of the NHS. In this information, the word ‘we’ refers to the NHS service that provides screening.

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This short animation explains screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome in pregnancy.

Down’s syndrome, Edwards’ syndrome and Patau’s syndrome video

1. Purpose of screening

To find out how likely it is that your baby has Down’s syndrome (Trisomy 21 or T21), Edwards’ syndrome (Trisomy 18 or T18) or Patau’s syndrome (Trisomy 13 or T13).

Screening is your choice. You do not have to have the screening test. Some people want to find out if their baby has one of the conditions and some do not. Screening is not perfect and might provide an incorrect result. It may lead to personal choices about your pregnancy.

If you choose to have screening, you can be screened for:

• all 3 conditions
• Down’s syndrome only
• Edwards’ syndrome and Patau’s syndrome only

This screening will be offered if you’re having one baby or twins.

2. Overview of screening

The screening process may involve several different tests.

The first screening test is called the combined test (or the quadruple test if you are later in your pregnancy). You may then be offered a second type of screening test called NIPT (non-invasive prenatal testing). Following either of these screening tests you may be offered a diagnostic test to confirm whether or not the baby has one of the conditions.

Find more information about Down’s syndrome, Edwards’ syndrome and Patau’s syndrome on the NHS website.

3. About these conditions

Inside the cells of our bodies there are tiny structures called chromosomes. These are made of DNA (genetic material). They carry the genes that determine how we develop. There are 23 pairs of chromosomes in each cell. Changes can occur in the sperm or egg cells, which can lead to a baby having an extra chromosome.

Babies with Down’s syndrome, Edwards’ syndrome or Patau’s syndrome are born to mothers of all ages but the chance of having a baby with one of the conditions increases as the mother gets older. They are all caused by having an extra copy of a chromosome in some or all cells of the body. Having the extra chromosome in just some cells is called the mosaic form and can lead to milder effects for the child. Screening cannot identify which form or what level of disability your baby will have.

3.1 Down’s syndrome (T21)

Down’s syndrome is caused by an extra copy of chromosome 21 in all or some cells of the body. A person with Down’s syndrome will have some level of learning disability. This means they will find it harder than most people to understand and to learn new things. They may have communication challenges and difficulty managing some everyday tasks. People with Down’s syndrome have distinctive facial features but they do not all look the same.

A child with Down’s syndrome

Most children with Down’s syndrome attend mainstream schools but will require additional support. Some health problems are more common in people with Down’s syndrome. These include heart conditions and problems with hearing and vision. Many health problems can be treated but unfortunately around 5% of babies will not live past their first birthday.

For babies without serious health problems survival is similar to that of other children and most people with Down’s syndrome will live into their 60s or longer.

People with Down’s syndrome can have a good quality of life and most say they enjoy their lives. With support, many more people with Down’s syndrome are able to get jobs, have relationships and live semi-independently in adulthood.

3.2 Edwards’ syndrome (T18) and Patau’s syndrome (T13)

Babies with Edwards’ syndrome have an extra copy of chromosome 18 in all or some cells. Babies with Patau’s syndrome have an extra copy of chromosome 13 in all or some cells.

Sadly the survival rates are low and of those babies born alive only around 13% with Edwards’ syndrome and 11% with Patau’s syndrome will live past their first birthday. Some babies may survive to adulthood but this is rare.

All babies born with Edwards’ syndrome and Patau’s syndrome will have a learning disability and a wide range of physical challenges, which can be extremely serious. They may have problems with their heart, respiratory system, kidneys and digestive system.

Around half of babies with Patau’s syndrome will also have a cleft lip and palate. Babies with Edwards’ syndrome and Patau’s syndrome will have a low birthweight.

Despite their difficulties, children can slowly make progress in their development. Older children with either condition would need to attend a specialist school.

Down’s syndrome occurs in 10 in every 10,000 births. Edwards’ syndrome occurs in 3 in every 10,000 births. Patau’s syndrome occurs in 2 in every 10,000 births.

4. The first screening test

If you choose to have the combined test, it will involve:

• a blood sample taken from your arm between 10 and 14 weeks of pregnancy
• an ultrasound scan measurement of fluid at the back of your baby’s neck between 11 and 14 weeks of pregnancy – this is known as the nuchal translucency (NT)

This information is combined with your age to work out the chance of your baby having the condition. If you are more than 14 weeks pregnant the combined test is not appropriate. You will instead be offered:

• a blood test, called the quadruple test, between 14 and 20 weeks of pregnancy to screen for Down’s syndrome (this test is not as accurate as the combined test)
• a 20-week scan to screen for Edwards’ syndrome and Patau’s syndrome

5. Safety of the test

The screening test cannot harm you or your baby but it is important to consider carefully whether or not to have this test.

The test cannot tell you if your baby definitely has one of these conditions. It can provide information that may lead to further decisions about your pregnancy.

If you receive a higher-chance result from the first screening test, you may need to decide whether to have a second screening test or a diagnostic test that has a risk of miscarriage. If you have a diagnostic test, depending on the result, you may need to decide whether to continue your pregnancy or have a termination.

6. Possible screening results

Depending on what you asked for when you decided to have the screening test, we will give you one or both of:

• a result for Down’s syndrome
• a joint result for Edwards’ syndrome and Patau’s syndrome

A lower-chance result means it is unlikely, though still possible, that your baby will have the condition. Most screening test results (around 97% of them) are lower chance.

A higher-chance result means it is more likely, but not certain, that your baby will have the condition. Overall, around 3% of screening test results are higher chance.

We will give each result as a chance, for example your baby has ‘1 chance in 150’ of being born with Down’s syndrome. The bigger the second number (such as 150), the smaller the chance your baby has of being born with the condition. So ‘1 chance in 200’ is smaller than ‘1 chance in 100’.

A ‘lower-chance’ result is 1 chance in 151 or more, for example 1 chance in 300. A ‘higher-chance’ result is 1 chance in up to 150, for example 1 chance in 100.

To understand what, for example, ‘1 chance in 300’ means, imagine a group of 300 women. One of these women will be pregnant with a baby that has the condition.

7. Not having the test

If you choose not to have the screening test for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome, the rest of your antenatal care will be unaffected.

Any scan during your pregnancy may pick up physical problems with your baby which could be related to these conditions. You will always be told if anything unexpected is found during a scan.

8. Getting my results

If your screening test shows a lower-chance result, you will be told within 2 weeks of the test being taken. If your screening test shows a higher-chance result, you will be told within a week of having the test. You will be offered an appointment to discuss:

• the test results and what they mean
• the condition your baby may have
• the choices available to you

9. Further tests

If you have a lower-chance result you will not be offered a further test. If you have a higher-chance result, you may decide:

• not to have any further testing
• to have a second screening test (called NIPT) to obtain a more accurate screening result before choosing whether or not to have a diagnostic test
• to have a diagnostic test straight away

Your decisions will be respected and health care professionals will support you. You should speak up if you feel your decisions are not being respected. Information is also available from support organisations. Whatever results you get from any of the screening or diagnostic tests, you will get support and care to help you decide what to do next.

10. The second screening test (NIPT)

The second screening test is another blood test called NIPT (non-invasive prenatal testing). NIPT is more accurate than the combined or quadruple test, though it is not quite as accurate in twin pregnancies. It works by measuring DNA (genetic material) in your blood. Some of this DNA will be from the baby’s placenta. If there is more DNA than expected from chromosomes 21, 18 or 13 it may mean that your baby has Down’s syndrome, Edwards’ syndrome or Patau’s syndrome. Like every screening test, though, it does not give a definite answer. NIPT cannot harm your baby. Most women will get their result within 2 weeks.

Most people will get a lower-chance result, meaning your chance of having a baby with the condition is low. You will not be offered a diagnostic test.

If your NIPT result shows a higher-chance result then the chance of your baby having the condition is high. You will then be offered a diagnostic test, though it is up to you whether or not to have this. In a small number of cases, NIPT might produce no result. You can then choose between one further NIPT, a diagnostic test or no further testing.

11. The diagnostic test (CVS or amniocentesis)

Diagnostic tests give a definite answer. They test cells from the placenta or fluid surrounding your baby.

Diagnostic tests can find conditions other than Down’s syndrome, Edwards’ syndrome or Patau’s syndrome but this is rare. 1 out of 200 women (0.5%) who have a diagnostic test will miscarry as a result of the test. There are 2 types of diagnostic test: chorionic villus sampling (CVS) and amniocentesis.

11.1 CVS (chorionic villus sampling)

This is usually done from 11 to 14 weeks of pregnancy but can be done later. A fine needle, usually put through the mother’s abdomen, is used to take a tiny sample of tissue from the placenta.

11.2 Amniocentesis

This is usually done after 15 weeks 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.

12. Results from the diagnostic test

Following the diagnostic test, some women will find out their baby has Down’s syndrome, Edwards’ syndrome or Patau’s syndrome. They can then choose to continue with the pregnancy or decide not to continue with the pregnancy and have a termination.

If you are faced with this choice you will get further information about the condition and support from health care professionals to help you make a decision.

Information is also available from support organisations.

Find more information and details of support organisations on the NHS website.

13. About this leaflet

With grateful thanks to the Down’s Syndrome Association for permission to use the photograph above.