Tests for Down’s syndrome

Here's what you need to know about screening and diagnostic tests for Down's syndrome in pregnancy

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As part of your NHS antenatal care, from about 12 weeks into your pregnancy, you will be offered various scans, checks and tests to make sure that your baby is healthy and developing well. One of the conditions that these tests can pick up is a genetic disorder called Down’s syndrome.

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You will be asked whether you want to have the checks for Down’s or not (you can refuse and no one will mind). So, scary as it is to think about the possibility of anything being ‘wrong’ with the baby you’re carrying, we reckon it’s worth arming yourself with all the info before you’re asked to make that decision.

What is Down’s syndrome?

Down’s syndrome, also known as trisomy 21 (T21), is a genetic disorder where a baby has an extra copy (or part of a copy) of chromosome 21. Children born with Down’s syndrome typically have some growth delays, and distinctive facial characteristics that often include eyes that slant upwards and outwards, and a small nose and mouth.

Anyone with Down’s syndrome will also have some mild to moderate learning disability, but the degree of learning disability varies widely from child to child (some will go on to attend mainstream schools, for example, while others will need more specialist educational support).

There is no cure for Down’s syndrome but many babies affected by it grow up to live happy, healthy and full lives – with, where it’s needed along the way, extra medical, or other specialist, help.

What are the odds of my baby having Down’s?

It’s thought to affect about 1 in every 500 pregnancies but the chances of it affecting yours are influenced by your age, with the risk steadily increasing the older you are. So, if you’re 20, the odds are roughly 1 in 1,500, but, if you’re 45, the odds come down to about 3 in 100.

Also, if you’ve previously had a baby with Down’s syndrome, you’re at a higher risk of it happening again: 1 in 100 women go on to have another child with the condition.

line of shoes

So, will the tests tell me for sure if my baby has Down’s?

No, not for absolute sure. Instead, you will be told the risk of your baby having Down’s, based on factors individual to you and your baby. And – here’s where it gets a bit complicated – because there are several types of test, the accuracy of the ‘risk result’ you’re given depends on which tests you’ve had.

Why are there several types of test? Because some are easier and quicker (and cheaper) to do and, if you get a ‘negative’ result from those, there’ll be no need to go on to have other more accurate but more complicated (and expensive) ones.

We think it helps to imagine the whole process as a series of sieves.

So, pretty much everyone has the 1st screening – or ‘sifting’. And most of us will pass through the sieve and be told our baby’s risk of Down’s is low. A few of us, however, will be left in the sieve, and told our baby seems to be at a higher risk of Down’s. We’ll be the ones who then go on (if we choose to) to the next sifting – through an even finer sieve. And so on.

sieve

What are the tests for Down’s syndrome?

There are currently 5 tests in all: 3 of them are called screening tests and 2 are diagnostic tests. The difference in names is all down to the accuracy of the test. So, a screening test will screen out anyone at low risk and flag up those at a higher risk (to differing degrees of accuracy), while a diagnostic test will give you such an accurate result (99%) that, if it’s positive for Down’s, doctors will view it as a diagnosis.

Are they all free on the NHS? All but 1 of these tests are available nationwide on the NHS. There are plans for the remaining 1 (called NIPT) to become available on the NHS some time in 2018 but, right now, it’s only offered in certain hospitals (although there are many clinics where you can pay for it privately).

Here’s what each of the tests are called, what they involve and when you’ll be offered it:

1. Combined test (screening test)

When do you have it? You’ll be offered this when you’re between 11 and 14 weeks pregnant. It’s called a combined test because it actually involves 2 separate screenings – and the results from these are combined together, along with the factors such as your age, to give you an overall result. You may find that, the way your hospital works, you have the 2 tests on different days.

What does it involve? The 2 screenings are a blood test and a nuchal translucency scan. With the blood test, a sample of your blood will be taken and then analysed for the levels of 2 particular proteins (hCG and PAPP-A). With the nuchal translucency (NT) test – which is done during your 1st routine pregnancy ultrasound scan (your ‘dating’ scan) – a measurement is taken of the amount of fluid that can be seen at the back of your baby’s neck.

Are there any risks with having this test? No.

Will I get this free on the NHS? Yes. But it’s only appropriate for women who are 14 weeks pregnant or less. If, for whatever reason, you’re over 14 weeks pregnant when you access antenatal care, you will be offered the Quadruple test (see below) instead.

When will I get the results? You may be told the NT test result on the day you have your scan. But the length of time it take to give you your final combined test results varies and, obviously, often depends on whether you have the 2 tests done on separate days, and how long your hospital takes to process all the information gathered by the tests. Generally speaking, you should hear between 1 to 3 weeks.

What will the results tell me? If you’re given the NT test result separately, you’ll be told the fluid measurement in millimetres: a measurement of 3.5mm or more suggests that your baby could be at increased risk of Down’s.

With the overall combined screening result, you’ll be given a risk ‘score’ that can range from 1 in 2 to 1 in 500 or more. Anything over 1 in 501 is considered low risk; anything between 1 in 2 and 1 in 500 is considered higher risk.

The combined test can also identify pregnancies at high risk of Edwards’ syndrome (trisomy 18) or Patau’s syndrome (trisomy 13), both rare but much more serious conditions than Down’s.

How accurate is it? The combined screening test picks up 85 to 90% of babies with Down’s syndrome (more than 4 out of 5). But in 2 out of every 100 tests, the result may indicate that your baby has Down’s syndrome, when he or she doesn’t (a ‘false positive’).

Will I need a further test? Only if your result is considered higher risk (and you want to keep on testing). If it is higher risk, you will be offered an appointment to discuss going on to have a diagnostic test (either amniocentesis or CVS), although you may be offered another (newer) screening called NIPT, or you may prefer to pay for a private NIPT if your hospital doesn’t offer one on the NHS.


blood sample on slide

2. Quadruple test (screening test)

When do you have it? Between 14 weeks 2 days, and 22 weeks 6 days of your pregnancy. It’s not suitable for anyone carrying twins or more, and it’s usually only offered to women who’ve missed the chance to have the combined screening test or where a measurement couldn’t be taken during the NT-test part of the combined screening can.

What does it involve? It’s a blood test, where a sample of your blood is taken and then analysed for the levels of 4 different hormones (AFP, beta HCG, inhibin-A, estriol). These results are the combined with your age, weight and the gestational age of your baby (how far along you are with your pregnancy, according to your dating scan).

Are there any risks with having this test? No.

Will I get this free on the NHS? Yes, if you are too far along for the combined test, or if your GP recommends it.

When will I get the results? Generally speaking, you should hear between 1 to 3 weeks.

What will the results tell me? You’ll be told whether your baby is low risk or higher risk (odds of 1 in 150 or greater) for Down’s. You will also be told if your baby is ‘screen positive’ or ‘screen negative’ for spina bifida (a spinal condition that can cause weakness and paralysis of the legs and, sometimes, bowel and bladder problems).

How accurate is it? The quadruple test picks up around 80% of babies with Down’s syndrome. But in 3 out of every 100 tests, the test result may indicate that your baby has Down’s syndrome when he/she doesn’t (a ‘false positive’). The test also picks up about 80% of babies with spina bifida.

Will I need a further test? Only if your result is considered higher risk for Down’s (or screen positive for spina bifida) and you want to keep on testing. If it is higher risk/screen positive, you will be offered an appointment to discuss going on to have a diagnostic test (either amniocentesis or CVS) or you may be offered another (newer) screening called NIPT. You could also pay for a private NIPT, if your hospital doesn’t offer one on the NHS.

dots of blood on testing slide

3. Non-Invasive Prenatal Testing or NIPT (screening test)

When do you have it? From the 10th week of pregnancy or after a combined screening/quadruple screening suggests your baby is at higher risk of Down’s.

What does it involve? NIPT, also known as cffDNA, is a blood test that offers a higher degree of accuracy in detecting Down’s (and Edwards’ and Patau’s) than the combined screening test or the quadruple screening test.

Will I get this free on the NHS? Probably not (yet). Some hospitals do offer NIPT for free but not all do – although there are plans to starting offering it at all hospitals from 2018. You may be able to have a NIPT at your hospital if you’re prepared to pay; alternatively, you could pay for it at one of the many private clinics that now offer it.

Are there any risks with having this test? No.

How long does it take to get the results? It varies according to where you have it done but the average wait is between 3 and 10 working days.

What will the results tell me? You will be given 1 of 3 possible results: positive (it’s highly likely your baby will have Down’s or another condition that a NIPT can detect); negative (it’s highly unlikely your your baby will have Down’s or another condition that a NIPT can detect), or inconclusive (usually becase there isn’t enough fetal DNA present in the sample to give an accurate result).

How accurate is it? NIPT detects around 98% of all babies with Down’s (and Edwards’ and Patau’s) syndrome. It can detect other conditions, though with a lower (and more varied) degree of accuracy.

Will I need a further test? Only if you get a positive result and you wish to carry on testing, or if you had an inconclusive result and wish to have (or are offered) another NIPT. If you had a NIPT on the NHS and get a positive result, you will be offered an appointment to discuss going on to have a diagnostic test (either amniocentesis or CVS). If you had a NIPT privately, you may be left to request a follow-up NHS appointment yourself.

More need-to-know facts about NIPT and how it works


woman talking to doctor

4. Chorionic villus sampling or CVS (diagnostic test)

When do you have it? Between 11 and 13 weeks (generally), if you agree to it and have had positive screening tests beforehand (or have had a child with Down’s before).

What does it involve? CVS is an invasive test where a doctor removes a small sample of your placenta either by putting a fine needle into your belly, or inserting a tube or forceps through your cervix. You’ll have an ultrasound scan beforehand to check on the position of your baby and your placenta.

Will I get this free on the NHS? Yes, if you’re offered it.

Are there any risks with having this test? There is a small (1 to 2%) risk of miscarriage.

How long does it take to get the results? The results usually come in 2 parts: a ‘rapid result’, usually available  after 3 working days, which should give a result for Down’s, and a fuller analysis, which usually takes 2 to 3 weeks, which may pick up other genetic abnormalities.

What will the results tell me? Most women get a ‘normal’ result. If your result is not normal, you will be told if the test has detected Down’s or any other chromosomal abnormality, including Edward’s, Patau’s, sickle cell disease, thalassaemia, cystic fibrosis and muscular dystrophy. Very occasionally (1 in 100 cases), women get an inconclusive result and may be offered an alternative procedure called amniocentesis

How accurate is it? CVS (and amniocentesis) are the most accurate tests available and, although they aren’t 100% accurate, they are so close (picking up 98 to 99% of babies with Down’s), that doctors regard a positive result as a definitive diagnosis.

Will I need a further test? No. If you get a positive result, you will offered the chance to discuss it with a specialist, and be supported to make a decision about whether to continue with your pregnancy or not.

CVS: should I have it, and what are my options?

5. Amniocentesis (diagnostic test)

When do you have it? Between about 15 and 20 weeks, if you agree to it and have had positive screening tests beforehand (or have had a child with Down’s before).

What does it involve? It’s called an ‘invasive’ test because, using an ultrasound probe for guidance, a doctor puts a very fine needle into your belly to remove a small sample of the amniotic fluid that’s surrounding your baby in your womb.

Will I get this free on the NHS? Yes, if you’re offered it.

Are there any risks with having this test? There is a very slight (0.5 to 1%) risk of miscarriage.

How long does it take to get the results? As with CVS,the results usually come in 2 parts: a ‘rapid result’, usually available  after 3 working days, which should give a result for Down’s, and a fuller analysis, which usually takes 2 to 3 weeks, which may pick up other genetic abnormalities.

What will the results tell me? Most women get a ‘normal’ result. If your result is not normal, you will be told if the test has detected Down’s or any other chromosomal abnormality, including Edward’s, Patau’s, sickle cell disease. muscular dystrophy and Tay Sachs. Very occasionally (1 in 100 cases), women get an inconclusive result and may be offered another amniocentesis.

How accurate is it? Amniocentesis (and CVS) are the most accurate tests available and, although they aren’t 100% accurate, they are so close (picking up 98 to 99% of babies with Down’s), that doctors regard a positive result as a definitive diagnosis.

Will I need a further test? No. If you get a positive result, you will offered the chance to discuss it with a specialist, and be supported to make a decision about whether to continue with your pregnancy or not.

Amniocentesis: should I have it and what are my options?

hands holding test tubes

And if I’m my baby does have Down’s, what then?

If you get a positive result for Down’s syndrome, you will be given some time to talk to a specialist healthcare professional (usually a midwife or a doctor who is experienced in childhood genetic conditions). They will give you more information about Down’s syndrome and how it might affect your baby, to help you decide whether you’d like to continue with your pregnancy or opt for a termination.

Obviously, this is a huge, and difficult, decision – particularly as, unlike babies with other, much more disabling genetic conditions, a baby with Down’s syndrome can be fit and healthy, and have no more health issues than any other child.

You shouldn’t feel any pressure to decide straightaway or to decide on your own. Take your time, and talk things over with your partner – and family and friends, if that would help.

As the info you get from the hospital is likely to be very factual and clinically based, you may feel you’d like to explore the practical and emotional side of what it’s like to raise a child with Down’s syndrome. If you think that would be helpful, the Down’s Syndrome Association has a booklet you can download and, on the MFM Chat forum, you can read Rachalow’s posts about her daughter Eloise.

Or you could ring the call the expert, impartial counsellors on the Antenatal Results and Choices helpline (open Monday to Friday, 10am to 5.30pm) on 0845 077 2290, or 0207 713 7486 from a mobile.

Do I have to have any of these tests?

No. Whether or not you have any of the tests or screenings that are offered to you throughout your pregnancy is entirely up to you. No one will try to persuade you one way or the other.

“Some women will not want to know that their baby has an anomaly,” says independent midwife Virginia Howes, author of The Baby’s Coming. “Others will want the information, either so they can choose to terminate the pregnancy or so they can be prepared for what may lie ahead caring for a sick or disabled child.”

These different approaches are summed up by 2 mums who post on our Chat forum.

Maxs mummy was in no doubt that she should have an amniocentesis, when it was offered. “My screening result came back as 1 in 40, so very high risk,” she says. “We chose to have the amnio. I felt like I needed the test because they had planted that seed of doubt in my mind. As it turns out, our baby is fine and the amnio came back clear.”

Dellamarie, by contrast, didn’t even consent to the combined screening test. “My midwife offered me the blood test,” she says, “but I refused and said, ‘What will be, will be.’ Our baby will not be loved any less.

“It’s definitely your choice. No one can force you.”

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