Screening for Down's, Edwards' and Patau's syndromes
Pregnant women are offered a screening test for Down's syndrome, Edwards' syndrome and Patau's syndrome from 10-14 weeks of pregnancy. This is to assess your chance of having a baby with these conditions.
Down's syndrome is also called Trisomy 21 or T21. Edwards' syndrome is also called Trisomy 18 or T18, and Patau's syndrome is also called Trisomy 13 or T13.
The screening test offered at 10-14 weeks is called the combined test. It involves a blood test and an ultrasound scan. All women in England are offered screening for Down’s, Edwards' and Patau's syndromes using this test.
If you are too far into your pregnancy to have the combined test, you will be offered other tests.
For Down’s syndrome, a blood test called the quadruple test is available from weeks 14-20 of pregnancy.
For Patau’s and Edwards’ syndromes, you will be offered a mid-pregnancy scan that checks for physical abnormalities.
If a screening test shows that you have a higher risk of having a baby with Down's, Edwards' or Patau's syndromes, you will be offered diagnostic tests to find out for certain if your baby has the condition.
What are Down's, Edwards' and Patau's syndromes?
Inside the cells of our bodies there are tiny structures called chromosomes. Chromosomes carry the genes that determine how we develop. There are 23 pairs of chromosomes in each cell.
Problems can occur when sperm or egg cells are produced, which can lead to a baby having an extra chromosome.
Read more about chromosomes.
In Down's syndrome, there is an extra copy of chromosome 21 in each cell. A baby born with Down's syndrome will have a learning disability. This means they will find it harder than most people to understand and learn new things. They may have communication problems and difficulty managing some everyday tasks.
It is impossible to know what level of learning disability a baby with Down's syndrome will have. It can vary from mild to severe. Most children with Down's syndrome attend mainstream primary school.
People with Down's syndrome can have a good quality of life. With support from their family and others, many people are able to get jobs and live fairly independently.
Some health problems are more common in people with Down's syndrome, such as heart conditions and problems with the digestive system, hearing and vision. Sometimes these problems can be serious, but many can be treated. With good healthcare, someone with Down's syndrome can live to around 60.
People with Down's syndrome have almond-shaped eyes and distinctive facial features, but they do not all look the same. Like all children, they also inherit features from their parents.
Read more about Down's syndrome.
Edwards' and Patau's syndromes
In Edwards' syndrome, there is an extra copy of chromosome 18 in each cell. In Patau's syndrome, there is an extra copy of chromosome 13 in each cell.
Sadly, most babies with Edwards' or Patau's syndromes will die before they are born or die shortly after birth. Some babies may survive to adulthood, but this is rare.
All babies born with Edwards' or Patau's syndromes will have a wide range of problems, which are usually very serious. These may include major brain abnormalities.
Babies affected by Edwards' syndrome can have heart problems, unusual head and facial features, growth problems, and be unable to stand or walk. Edwards' syndrome affects about 3 out of every 10,000 births.
Babies affected by Patau's syndrome can have heart problems, a cleft lip and palate, growth problems, poorly formed eyes and ears, problems with their kidneys, and be unable to stand or walk. Patau's syndrome affects about 2 out of every 10,000 births.
Read more about Edwards' syndrome and Patau's syndrome.
What does screening for Down's, Edwards' and Patau's syndromes involve?
A screening test for Down's, Edwards' and Patau's syndromes is available from weeks 10-14 of pregnancy. It is called the combined test because it combines an ultrasound scan with a blood test. The scan can be carried out at the same time as the pregnancy dating scan.
If you choose to have the test, a blood sample will be taken from you. At the scan, the fluid at the back of the baby's neck is measured (known as the nuchal translucency). Your age and the information from these two tests is used to work out the risk of the baby having Down's syndrome, or Edwards' or Patau's syndromes.
It is not always possible to obtain a nuchal transparency measurement, and depends on the position of the baby. If this is the case, you will be offered a different blood screening test to take place from weeks 14-20.
If you are too far on in your pregnancy (more than 14 weeks) to have the combined test, you will be offered a test called the quadruple blood screening test from 14-20 weeks of pregnancy. This blood test only screens for Down’s syndrome and is not quite as accurate as the combined test.
For Edwards' and Patau's syndromes, if you are too far into your pregnancy to have the combined test, you will be offered a mid-pregnancy scan. This scan looks for physical abnormalities and 11 rare conditions, including Edwards’ and Patau’s syndromes.
Can this screening test harm me or my baby?
The screening test cannot harm you or the baby, but it is important to consider carefully whether to have this test. It cannot tell you for certain if the baby has or does not have Down's, Edward's or Patau's syndromes.
The test can provide information that may lead to further important decisions. For example, you may be offered diagnostic tests that can tell you for certain whether the baby has these conditions, but these tests have a risk of miscarriage.
Do I need to have screening for Down's, Edwards' or Patau's syndromes?
You do not need to have this screening test – it is your choice whether or not to have it. Some people want to find out the risk of their baby having these conditions, and some do not.
You can choose to have screening for:
- all the conditions (Down's, Edwards' and Patau's syndromes)
- Down's syndrome only
- Edwards' and Patau's syndromes only
- none of the conditions
What if I decide not to have this test?
If you choose not to have the screening test for Down's, Edwards' or Patau's syndromes, you can still choose to have other tests, such as a dating scan.
If you choose not to have the screening test for these conditions, it is important to understand that if you have a scan at any point during your pregnancy, it could pick up physical abnormalities.
The person scanning you will always tell you if any abnormalities are found.
Getting your results
The screening test will not tell you if your baby has or does not have Down's, Edwards' or Patau's syndromes. It will tell you if you have a higher or lower risk of having a baby with one of these conditions.
If you have screening for all three syndromes, you will receive one risk for Down's syndrome and one combined risk for Edwards' and Patau's syndromes (two risks altogether).
If your screening test shows a lower-risk result, you should be told within two weeks of the test being taken. If your screening test shows a higher-risk result, you should be told within three working days of the blood test result being available.
This may take a little longer if your test is sent to another hospital. It may be worth asking the midwife what happens in your area and when you can expect to get your results. You will be offered an appointment to discuss the test results and the options you will have.
The charity Antenatal Results and Choices (ARC) offers lots of information about screening results and the options you face if you get a higher-risk result. There is also an ARC forum, where you can be put in touch with people who are in the same situation as you. You can read about people's experiences of deciding to continue a pregnancy on the ARC website.
If the screening test shows that the chance of having a baby with Down's, Edwards' and Patau's syndromes is lower than 1 in 150, this is a lower-risk result. More than 95 out of 100 screening test results (95%) will be lower risk. A lower-risk result does not mean there is no risk at all of the baby having Down's, Edwards' or Patau's syndromes.
If the screening test shows that the chance of the baby having Down's, Edwards' or Patau's syndromes is higher than 1 in 150 (that is, between 1 in 2 and 1 in 150), this is called a higher-risk result.
Fewer than 1 in 20 test results (5%) will be higher risk. This means that out of 100 women accepting screening for Down's, Edwards' and Patau's syndromes, fewer than 5 will have a higher-risk result. A higher-risk result does not mean the baby definitely has Down's, Edwards' or Patau's syndromes.
Will I need further tests?
If you have a lower-risk result, you will not be offered a further test. If you have a higher-risk result, you will be offered a diagnostic test, such as amniocentesis or chorionic villus sampling (CVS). This will tell you for certain whether the baby has Down's, Edwards' or Patau's syndrome or not.
About 0.5 to 1 in 100 diagnostic tests (0.5 to 1%) result in a miscarriage. It is up to you whether or not to have the further tests. When trying to decide whether to have a diagnostic test, try to balance up the risk of miscarriage with how important the result will be to you.
Chorionic villus sampling (CVS)
This diagnostic test is usually done from weeks 11-14 of pregnancy. A fine needle, usually put through the mother's abdomen, is used to take a tiny sample of tissue from the placenta. The cells from the tissue are then tested for Down's, Edwards' or Patau's syndromes.
Read more about CVS.
Amniocentesis is done from around week 15 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. The fluid contains cells from the baby, which are tested for Down's, Edwards' or Patau's syndromes.
Read more about amniocentesis.
If you find out your unborn baby has Down's, Edwards' or Patau's syndrome
A small number of women who have a diagnostic test will find out their baby has Down's, Edwards' or Patau's syndrome. They then have two options.
Some women decide to continue with the pregnancy and prepare for their child with the condition; others decide they do not want to continue with the pregnancy and have a termination (abortion).
If you are faced with this choice, you will get support from health professionals to help you make your decision. You can get more information from the charity Antenatal Results and Choices (ARC), which runs a helpline (Mon-Fri) on 0845 077 2290 or 020 7137 7486 from a mobile.
The Down's Syndrome Association also has useful information on screening, and the UK National Screening Committee has produced a booklet called Screening tests for you and your baby.
The charity SOFT UK offers information and support through diagnosis, bereavement, pregnancy decisions and caring for all UK families affected by Edwards' syndrome (T18) or Patau's syndrome (T13).