What is Down's syndrome?
Down's syndrome is caused by an abnormal number of chromosomes. It affects around one in every 1,000 babies, which means that about 600 babies with Down's syndrome are born each year in the UK.
There's no such thing as a typical person with Down's syndrome. Like everyone, people with Down's syndrome vary a lot in appearance, personality and ability. People with Down's syndrome have learning difficulties and some have more serious difficulties than others. It's hard to tell how much Down's syndrome babies will be affected as children or adults. There is currently no cure for the condition, but there are treatments that can help someone with the syndrome lead an active and independent life.
Conditions linked with Down’s syndrome include heart problems and reduced hearing and vision. Many of these problems can be treated, and frequent health checks can ensure that any problems are detected as early as possible. Most people with Down’s syndrome live to around 60, and some live to be over 70.
What causes Down’s syndrome?
Inside the cells of our bodies are tiny structures called chromosomes. Chromosomes carry the genes that determine how we develop. Most people have 23 pairs of chromosomes in each of their cells. When our bodies produce the sperm and egg cells needed to create babies during reproduction, the chromosome pairs divide and rearrange themselves. Sometimes these pairs don't divide correctly, and this causes the baby’s cells to have an extra copy of chromosome number 21. This causes Down’s syndrome.
The extra chromosome can't be removed from cells, so there's no cure for the condition. The chromosomes divide incorrectly by accident, not because of anything the parents have done.
Some people think that only older women can have a baby with Down’s syndrome, but this is not true. Anyone can have a baby with Down’s syndrome, but the risk increases with age. The older a mother is, the more likely she is to have a baby with the condition.
Screening
Screening for Down's syndrome and other genetic disorders is offered to all pregnant women. There are different ways of carrying out screening tests.
Combined screening
This involves a blood test and an ultrasound scan. All women should have dating and nuchal translucency scans between 8-14 weeks of pregnancy. These scans may be combined. The blood test measures two blood chemicals associated with pregnancy. At the ultrasound, the radiographer measures the thickness of the nuchal translucency (a pocket of fluid) at the back of your baby's neck. This information is used to calculate your individual chance of having a baby with Down's syndrome. This nuchal translucency scan can be used in multiple pregnancies (if you're having twins or more).
Serum screening
Serum screening is a blood test that screens for Down's syndrome, usually when you are around 16 weeks pregnant. It measures three or four blood chemicals that are associated with pregnancy, and this can be used to work out your individual chance of having a baby with Down's syndrome. Serum screening is not used for pregnancies of twins, triplets or more.
Screening results
Some maternity services give the result as 'lower risk/screen negative' or 'higher risk/screen positive'.
If the screening test shows the risk of the baby having Down's syndrome is lower than the recommended national cut-off level for risk, this is known as having a low-risk result. A low-risk result means that you are at a low risk of having a baby with Down's syndrome, but it doesn't mean that there is no risk at all.
If the result shows the risk of the baby having Down's syndrome is greater than the recommended national cut-off level for risk, this is known as an increased risk, or higher risk, result. An increased risk means you will be offered diagnostic tests but it does not mean that your baby definitely has the condition.
The diagnostic procedure you will be offered is either chorionic villus sampling (CVS) or amniocentesis, which will give you a definite answer about Down's syndrome.
Your midwife or doctor will explain the result to you and help you to decide whether you want to have further testing.
