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

1. Purpose of screening

The purpose of this screening is 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.

2. Overview of screening

The screening process may involve several different tests.

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

3. About these conditions

Inside the cells of our bodies there are tiny structures called chromosomes. These are made of DNA (genetic material). These chromosomes carry the genes that determine how we develop. There are typically 23 pairs of chromosomes in each cell. Changes can take place 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 women of all ages. However, 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 of the body’s cells. Having the extra chromosome in just some cells is called the mosaic form. This 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 go to mainstream schools but will need extra 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 conditions can be treated. Unfortunately, around 5 out of every 100 babies (5%) will not live past their first birthday.

For babies without serious health problems survival rates are similar to those of other children. 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 people with Down’s syndrome can 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. Of those babies born alive, only around 13 out of every 100 (13%) with Edwards’ syndrome and 11 out of every 100 (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 learning disabilities and a wide range of health challenges. Some of these can be extremely serious. They may have problems with their heart, respiratory system, kidneys or 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 may have a low birthweight.

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

4. NHS combined and quadruple screening tests

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

• a blood test between 10 and 14 weeks of pregnancy
• an ultrasound scan between 11 and 14 weeks of pregnancy to measure the fluid at the back of your baby’s neck - 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 the quadruple test. This involves a blood test between 14 and 20 weeks of pregnancy. The test screens for Down’s syndrome only and is not as accurate as the combined test.

You will be offered a 20-week screening scan to screen for Edwards’ syndrome and Patau’s syndrome.

5. Safety of the test

The screening test cannot harm you or your baby. However, 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.

6. Screening is your choice

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.

You can choose to have:

• no screening
• screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome
• screening for Down’s syndrome only
• screening for Edwards’ syndrome and Patau’s syndrome only

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

If you have a vanished twin pregnancy, your midwife or doctor will discuss your testing options with you.

7. Possible 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 any of the conditions screened for. Most screening test results are lower chance.

Most women with higher chance results will have a baby without any of the conditions. Some women will have a higher chance result for one of the conditions and the baby will have a different condition. For example, if you have a higher chance result for Down’s syndrome, there is a chance that the baby has Patau’s syndrome. Overall, around 3 out of every 100 screening test results are higher chance.

You will receive 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.

8. Not having the test

If you choose not to have the screening test for these conditions, the rest of your antenatal care will continue as planned.

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

9. 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

10. 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 will be offered:

• no further testing
• a second screening test (called NIPT) to get a more accurate screening result before choosing whether to have a diagnostic test
• a diagnostic test

If you have a very high chance result (between 1 in 2 and 1 in 10) from your first screening test, you should have an in-depth discussion with a healthcare professional about your options. This is because NIPT is less accurate when you receive a very high chance result for Edwards’ syndrome or Patau’s syndrome.

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.

11. Non-invasive prenatal testing (NIPT)

You may be offered a second screening test called NIPT, which involves a blood test.

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 women will get a lower chance result, meaning your chance of having a baby with any of the conditions 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 any of the conditions is high. You will then be offered a diagnostic test, and it is up to you whether you choose 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.

The laboratory may keep your NIPT screening sample for up to 5 years. This is for quality and testing purposes. If you do not wish your sample to be kept, let your healthcare professional know.

12. The diagnostic test (chorionic villus sampling or amniocentesis)

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

Diagnostic tests can sometimes find conditions other than Down’s syndrome, Edwards’ syndrome or Patau’s syndrome. However, this is rare.

About 1 out of 200 women (0.5%) who have a diagnostic test will miscarry because of the test. It is up to you whether you have the diagnostic test.

There are 2 types of diagnostic test: chorionic villus sampling (CVS) and amniocentesis.

12.1 Chorionic villus sampling (CVS)

This is usually done from 11 to 14 weeks of pregnancy but can be done later. A fine needle is used to take a small sample of tissue from the placenta. The needle is usually put through the woman’s abdomen (tummy). The cells from the placenta can be tested for the conditions screened for.

12.2 Amniocentesis

This is usually done after 15 weeks of pregnancy. A fine needle is used to collect a small sample of the fluid surrounding the baby. The needle is passed through the woman’s abdomen (tummy). The fluid contains some of the baby’s cells, which can be tested for the conditions.

13. 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, healthcare professionals will support you and give you further information about the condition to help you decide.

Information is also available from support organisations.

14. About this leaflet

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