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

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  1. 1. Overview
  2. 2. The screening tests
  3. 3. Getting the results
  4. 4. Your choices

Overview

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.

Whether you want to know this will be personal to you. It’s your choice whether to have the screening or not.

In the UK:

  • around one baby in every 700 births has Down’s syndrome - it’s the most common chromosomal condition
  • around one baby in every 5000 births has Edwards’ syndrome - it’s the second most common chromosomal condition
  • around one 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 do not want them.

Twin pregnancies

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.

Chromosomes explained

Chromosomes carry genes that determine how we develop. People usually have 46 chromosomes, 23 from the mother and 23 from the father.

Down’s syndrome, Edwards’ syndrome and Patau’s syndrome are separate conditions that 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.

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

The screening tests

You’ll be offered either:

  • a blood test combined with an NT ultrasound scan (if you’re between 11 weeks and 14 weeks pregnant)
  • a blood test on its own for Down’s syndrome only (if you’re between 14 weeks and 20 weeks pregnant)

Your midwife will explain which tests you can have.

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 health professional if you smoke.

You should also speak to your health professional if you have had an assisted pregnancy such as in-vitro fertilisation (IVF).

This is because your age and the age of the egg donor are used in the calculation. Having this information can give a more accurate screening result.

NT ultrasound scan

The NT (nuchal translucency) 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.

Getting the results

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 sample
  • your age, weight and stage of pregnancy
  • other information

What happens if I choose to be screened for Down’s syndrome and/or Edwards’ syndrome and Patau’s syndrome?

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.

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’ll not be offered further tests.

More than 95% of screening test results show the chance of the baby having Down’s syndrome, or Edwards’ syndrome and 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 further choices are.

You’ll be given time to think through your choices and reach decisions which feel best for you and your baby. You do not need to make any decisions straight away.

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 Down’s syndrome, Edwards’ syndrome or Patau’s syndrome.

Your choices

People choose to have further tests or not for lots of different reasons and your choices will be personal.

Whatever choice you make regarding further testing will be respected and supported.

No one will ever test you without being sure you know what the test is for, how it’s done, and that you’re prepared to have it.

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

Your midwife will respect your choices whether you choose to have more tests or not and will keep your choices private.

They’ll look after you and your baby and will tell you about support organisations that can help you and give you more information.

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