Information about antenatal screening tests - Section 6 – Screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome

This section explains the tests that can be done during pregnancy to find out if your baby has Down’s syndrome (trisomy 21 or T21), Edwards’ syndrome (trisomy 18 or T18) or Patau’s syndrome (trisomy 13 or T13). Women who find out that their baby has a higher chance of these conditions will be offered a further screening test or an invasive procedure, such as chorionic villus sampling (CVS) or amniocentesis (see section 7).

You can choose whether or not to have these tests. Some women want to find out if their baby has one of the conditions and some do not.

This animation gives information on the screening tests you will be offered during pregnancy for you and your baby.

What is Down’s syndrome? (T21)

Down’s syndrome is caused by an extra copy of chromosome 21 in all or some cells of the body. 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 are able to get jobs, have relationships and live semi-independently in adulthood.

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. Most children with Down’s syndrome attend mainstream schools but need additional support. People with Down’s syndrome are more likely to have some medical conditions, including heart conditions. Many of these conditions can be treated, with good outcomes.

You can choose whether or not to have these tests. Some women want to find out if their baby has one of the conditions and some do not. In Wales, 90% (9 in 10) children with Down’s syndrome live past their fifth birthday. For babies without serious health conditions, survival rates are similar to that of other children. With good health care, most people will live into their 60s. 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.

Down’s syndrome happens in 1 in 415 pregnancies in Wales.

You can view family stories about living with Down’s syndrome on the Antenatal Screening Wales website.

You can get more information about Down’s syndrome from: NHS 111 Wales – Health A-Z : Down’s syndrome.

What are 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 in Wales, only around 13% (1 in 7) 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 conditions affecting their heart, limbs, kidneys and digestive system.

Around half of babies with Patau’s syndrome will 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. All women have a chance of having a baby with Edwards’ syndrome or Patau’s syndrome. The chance increases with age but babies are also born with these conditions to younger women. This is why women of all ages are offered the screening test.

Edwards’ syndrome happens in about 1 in 1656 pregnancies in Wales and Patau’s syndrome in 1 in 4201.

You can view family stories about living with Edwards’ syndrome on the Antenatal Screening Wales website.

You can get more information about Edward’s syndrome and Patau’s syndrome from: NHS 111 Wales – Health A-Z : Edwards’ syndrome (trisomy 18).

NHS 111 Wales – Health A-Z : Patau’s syndrome

What screening test will I be offered?

Combined screening – this test is taken between 11 and 14 weeks of pregnancy

You will be offered an ultrasound scan (if possible, the sonographer will measure the small collection of fluid (nuchal translucency) at the back of the baby’s neck). 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 and the chance of your baby having Edwards’ syndrome or Patau’s syndrome.

Sometimes the measurements can be difficult to get. For example, the baby may be lying in the wrong position or you may be above average weight for your height and this makes looking at the 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 you are having twins, you will be offered the combined screening test. The quadruple screening test is not offered in Wales in twin pregnancies as it is not as accurate as in single pregnancies.

Quadruple screening – this test is taken between 15 and 18 weeks of pregnancy

You will be offered a quadruple test if the measurements that are needed cannot be taken or if you go for the scan appointment later than 14 weeks pregnant. This involves having a blood test to find out your chance of having a baby with Down’s syndrome but not Edwards’ syndrome or Patau’s syndrome.

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

What will the screening test result tell me?

The screening test can tell you what chance you have of your baby having one of the conditions.

The combined test

This is taken before on or before you are 14 weeks and 1 day pregnant.
If you have the combined test you will get two different results:
- One will tell you your chance of your baby having Down’s syndrome.
- The other will tell you your chance of your baby having Edwards’ syndrome or Patau’s syndrome.

The quadruple test

This is taken at around 16 weeks of pregnancy (but can be taken between 15 weeks and 0 days and 18 weeks and 0 days pregnant) and will only tell you your chance of having a baby with Down’s syndrome.

The screening test does not identify all babies with these conditions. For example, on average, 70% to 80% (seven or eight babies in 10) of babies with these conditions will be identified by screening. This means 20% to 30% (around two or three in 10) of babies with these conditions will not be identified by the screening test.

What are the advantages of having screening for these conditions?

If your baby has one of these conditions, 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 one of these conditions or to end your pregnancy.

What are the disadvantages of having screening for these conditions?

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 one of these conditions. ‘Higher chance’ is how we describe your result if it is between 1 in 2 and 1 in 150.

If the result is between 1 in 2 and 1 in 150, you will be offered either:

no further testing
another screening test called non-invasive prenatal testing (NIPT), which is more accurate than the combined or quadruple test, or
an invasive test to see if your baby definitely has one of these conditions.

Because the invasive test, called amniocentesis or chorionic villus sampling (CVS), has a small chance of causing a miscarriage, many women find this a difficult decision.

Should I have the screening test for Down’s syndrome (T21), Edwards’ syndrome (T18) and Patau’s syndrome (T13)?

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

Your decision will be respected and health-care professionals will support you whatever you decide. The scans you have in pregnancy can occasionally see things that may identify that your baby could have one of these conditions and you may be offered an invasive test at this stage.

Results

The results are given as either ‘higher chance’ or ‘lower chance’.

What happens if I have a lower chance result?

If your test result shows you have a lower chance of having a baby with Down’s syndrome, Edwards’ syndrome or Patau’s syndrome, no more tests are offered.

Please remember that having a lower chance does not mean that you have no chance of having a baby with one of these conditions.

What happens if I have a higher chance result?

If your test result shows you have a higher chance of having a baby or babies with one of the conditions screened for (that is, a chance of 1 in 2 to 1 in 150), you will be offered an appointment with a midwife or hospital doctor (obstetrician). 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 more accurate screening test called a non-invasive prenatal test (NIPT), or an invasive procedure (CVS or amniocentesis), which will give you a definite result but has a small risk of miscarriage. You may face some difficult decisions after an invasive 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 your baby having Down’s syndrome than 1 in 140

Between 2% and 4% of women (between two and four in 100) of women who have the combined or quadruple screening tests have a result which shows they have a higher chance of having a baby with one of these conditions.

Non-invasive prenatal test (NIPT)

NIPT is a further screening test and will not give a definite result. However, it is more accurate than the combined or quadruple test. It is a blood test taken from you in the usual way – your blood will have some of your baby’s DNA (genetic material from the placenta) in it. The laboratory screens this blood sample to tell you if there is a ‘high’ or ‘low’ chance that your baby has Down’s syndrome, Edwards’ syndrome or Patau’s syndrome.

If you choose this test it usually takes about two weeks to get the result. In about 0.3% (1 in 300) of pregnancies of cases the NIPT test will not be able to give a result and you will be offered an invasive test or you may decide to have no further tests.

If the NIPT result is high chance you will be offered an invasive test to tell you for definite if your baby has one of the three conditions. If you choose not to have an invasive test you will be supported in your decision, and we can give you as much information as you want about the syndrome that the NIPT is high chance for. If the NIPT is low chance, it is unlikely that your baby will have Down’s syndrome, Edwards’ syndrome or Patau’s syndrome and you will not be offered any further testing.

What invasive procedures will I be offered if I have a higher or high chance screening result?

Depending on how many weeks pregnant you are, you will be offered either a chorionic villus sampling (CVS) or amniocentesis procedure (see section 7)

What would an invasive test result tell me?

The result would tell you if your baby or babies have Down’s syndrome, Edwards’ syndrome or Patau’s syndrome. If your baby or babies have one of these conditions, you can decide whether to prepare for the birth of your baby or to end your pregnancy.

Accessible resources are available for this section

Page last reviewed: 11th May 2026