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Testing for Downs Syndrome

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What is Down’s syndrome?

Down’s syndrome affects around one in every 1,000 babies born. As they grow up, these babies will have learning difficulties. These difficulties vary hugely and while some people are affected quite severely, others will be able to live relatively ‘normal’ lives. Health conditions linked to Down’s syndrome include heart conditions and problems with hearing and sight. However, these can usually be treated and should be picked up early through routine health checks.

What are the causes?

Most people have 23 pairs of chromosomes in each of their cells. Down’s syndrome occurs when the sperm and egg are creating cells and an extra copy of one of these chromosomes – chromosome 21 – is produced. This is a natural occurrence and isn’t related to anything the parents may have or have not done. While it is widely accepted that the chances of having a child with Down’s syndrome increase with the mother’s age, over half of babies with the condition are born to mothers under 35 years old.

What can a test tell me?

All pregnant women are offered screening for Down’s syndrome. Whether you choose to take part or not is entirely up to you and your partner. Your midwife will give you any information you may need to help make the decision. Screening cannot tell you for definite whether or not your child has Down’s syndrome but rather show how likely it is that your child may have it. If the test comes back as a lower-risk result then the chance that your baby will be born with the condition is lower than 150 to one. A higher-risk result means the chances are higher than one in 150 and you will be offered a diagnostic test to further investigate. This doesn’t mean your baby has Down’s syndrome, it just means there is a higher chance of it. A diagnostic test can let you know one way or the other.

Screening tests

born with a disabilityThe most common screening test for Down’s syndrome is a blood test and nuchal translucency scan, which is usually done at the same time as your dating scan. Your blood is tested for two proteins associated with pregnancy and the sonographer will measure the thickness of the nuchal translucency (fluid at the back of your baby’s neck). The results of both tests will be combined with your age to determine the likelihood of your child being born with Down’s syndrome.

If it hasn’t been possible for you to have a screening test at your dating scan – because you didn’t find out you were pregnant until later, for example – your midwife will offer a quadruple blood test. This checks four proteins associated with pregnancy and is again combined with your age to produce your individual risk.

Diagnostic tests

Diagnostic tests are offered to women whose screening tests come back in the higher-risk category. As with screening tests, you can opt out if you’d prefer. Diagnostic tests carry a 0.5 to 1% chance of miscarriage, which although relatively small, is worth taking into account when making your decision. There are two types of diagnostic tests. Amniocentesis can be used from the 15th week of the pregnancy and involves a fine needle being inserted through the abdomen to withdraw a small amount of amniotic fluid, which is then tested. The other type of test is called corionic villus sampling (CVS) and is effective from around 11 weeks. CVS is similar to amniocentesis but involves a tiny piece of the placenta being removed for testing, rather than amniotic fluid. It is generally more uncomfortable and so a local anaesthetic will normally be used. Both tests take around 5-10 minutes and results should be available three to four days later.

What if the test detects an abnormality?

Discovering your baby has Down’s syndrome can come as a shock. You may know little about the condition and have a tonne of questions to ask before you can make an educated decision about which is the best way forward for you and your family. Your midwife will provide you with plenty of information on Down’s syndrome and will be able to point you in the right direction for support and advice. You may find speaking to other parents that have been in the same situation can help. There is no cure for Down’s syndrome but pre-natal testing can allow you to get over any initial shock early so you can enjoy getting to know your newborn baby.

 

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About Maria Brett

About Maria Brett

Maria is a freelance writer with over 10 years' experience producing content for a variety of publications and websites. When not working or looking after her two gorgeous sons, she can usually be found playing flugelhorn in a brass band, helping out at her local hospital radio station, shouting at the television while watching Formula 1, at the cinema or plonked on the couch with a cold glass of wine.

Website: Maria Brett

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