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

You’ll be offered screening to find out how likely it is that your baby may have Down’s syndrome, Edwards’ syndrome, or Patau’s syndrome.

In the UK:

• around 1 baby in every 700 births has Down’s syndrome - it’s the most common chromosomal condition
• around 1 baby in every 5000 births has Edwards’ syndrome - it’s the second most common chromosomal condition
• around 1 baby in every 16,000 births has Patau’s syndrome

Choosing which to be screened for

During the first trimester you can choose to be screened to find out if your baby may have:

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

You can choose not to have any of these screening tests if you don't want them.

Pregnancies with more than one baby

You’ll be offered the same screening choices if you’re pregnant with twins as you would be if you were pregnant with one baby.

Screening tests may be less accurate with twin pregnancies.

Your midwife will help you to understand what this means and support you to decide if choosing further tests feels right for you and your babies.

NIPT is not suitable for triplet pregnancies, or pregnancies with more than 3 babies.

Chromosomes explained

Our bodies are made from millions of cells, and inside every cell there are chromosomes. Chromosomes carry genes that determine how we develop.

People usually have 46 chromosomes, 23 from the mother and 23 from the father. If babies have an extra full or partial chromosome in their cells, they’ll have a chromosomal condition. If this is only in some of their cells, it may be called mosaicism.

Down’s syndrome, Edwards’ syndrome and Patau’s syndrome are separate conditions. Most forms of chromosomal conditions happen by chance. They’re not caused by anything parents do before or during pregnancy.

Older mothers are more likely to have a baby with one of the conditions and the chance increases with the mother’s age at pregnancy. But Down’s syndrome, Edwards’ syndrome and Patau’s syndrome can occur in pregnancy for women of any age.

All pregnant women, no matter what age, can have the test.

Read more about Down’s syndrome

Read more about Edwards’ syndrome

Read more about Patau’s syndrome

If you're between 11 and 14 weeks pregnant, you'll be offered a blood test combined with a nuchal translucency (NT) ultrasound scan.

If you're between 14 and 20 weeks pregnant, you'll be offered a blood test on its own for Down’s syndrome only.

Some tests can only be done at certain times during pregnancy. If your early pregnancy scan shows you’re at a different stage of pregnancy than you thought, your midwife will explain which tests you can have.

If you’re not able to have first trimester screening for Down’s syndrome, Edwards’ syndrome, and Patau’s syndrome, you can only have screening for Down’s syndrome during the second trimester.

The blood test

The blood test measures substances that have passed between you and your baby.

If you decide to have the test, a sample of your blood will be taken between 11 and 20 weeks.

You should speak to your healthcare professional if you:

• smoke
• have an assisted pregnancy, for example in vitro fertilisation (IVF)

Your age and (if relevant) the age of the egg donor are used to calculate your result. Having this information can give a more accurate screening result.

Nuchal translucency ultrasound scan

The nuchal translucency (NT) ultrasound scan is carried out between 11 and 14 weeks of pregnancy, usually as part of your early pregnancy screening scan.

It’s sometimes called the ‘combined’ test because it combines the results from the scan with your blood test.

The ultrasound measures the amount of fluid lying under the skin at the back of your baby’s neck.

Read more about the nuchal translucency scan

You may have chosen to be screened for Down’s syndrome only, Edwards’ syndrome and Patau’s syndrome only, or all three conditions. You’ll only receive the results you’ve asked for.

A computer works out the chance of your baby having Down’s syndrome or a combined chance of Edwards’ syndrome and Patau’s syndrome using:

• your NT ultrasound scan and blood test
• your age, weight and stage of pregnancy
• other information (for example, whether you smoke or not)

If I get a lower-chance result

Most women will get a lower-chance result. This means it’s unlikely your baby has Down’s syndrome, Edwards’ syndrome or Patau’s syndrome. It usually means your baby has a chance lower than 1 in 150 of having one of the conditions.

If the screening test shows the chance of your baby having Down’s syndrome, Edwards’ syndrome or Patau’s syndrome is low, you won't be offered further tests.

More than 95% of screening test results show the chance of the baby having either Down’s syndrome, Edwards’ syndrome or Patau’s syndrome is low. It does not mean there’s no chance at all that the baby has one of these conditions, just that it’s unlikely.

If I get a higher-chance result

If you get a higher-chance result, it doesn't mean your baby definitely has Down’s syndrome, Edwards’ syndrome or Patau’s syndrome, but it’s more likely. It usually means your baby has a chance higher than 1 in 150 of having one of the conditions.

I have a higher-chance result, what happens next?

Your midwife will discuss your results with you and explain what they mean. They’ll then tell you what your choices are.

After a higher-chance result, you’ll be offered a choice of having:

• no further tests
• a further screening test - non-invasive prenatal testing, known as NIPT
• a diagnostic test - chorionic villus sampling (CVS) or amniocentesis

Further testing can give you more accurate information about how likely it is your baby may have either Down’s syndrome, Edwards’ syndrome or Patau’s syndrome.

You’ll be given time to think through your choices and decide what's best for you and your baby. You don't need to make any decisions straight away.

Your choices

People choose to have further tests or not for lots of different reasons, and your choices will be personal. Your midwife will respect your choices and will keep them private.

Tell your midwife if at any point you’re not sure about the choices you’ve made or if you’d like more information.

Results from further testing may affect whether you decide to continue or end your pregnancy. You may wish to get information to help you prepare for a baby who may need additional care and support.

Your midwife will tell you about support organisations that can help you and give you more information.