Down syndrome is a genetic condition causing mild-moderate intellectual disability, typical facial features, and physical growth delays. The disorder is also known as 'trisomy 21' as it involves the presence of an extra copy of chromosome 21.

What causes Down syndrome?

Down syndrome is caused by abnormalities with how cells divide in early development. Inside the cells of our bodies are tiny packages called 'chromosomes' that carry genes to determine how we develop. Most people have 23 pairs of chromosomes in each of their cells. In people with Down syndrome these pairs don't divide correctly, resulting in an extra copy of chromosome 21. This means the baby's cells have 47 chromosomes instead of 46, and this impacts physical and mental development.

There is no known reason why the chromosomes divide incorrectly. It occurs by accident at conception (when the egg is fertilised by the sperm), not because of anything the parents have done.

Although the chance of having a child with Down syndrome increases with the age of the mother, anyone can have a baby with Down syndrome. It affects about one in every 700-900 babies. There are over 15,000 people in Australia living with Down syndrome, across all ethnic and social groups.

Living with Down syndrome

Down syndrome is a life-long condition. The extra chromosome 21 can't be removed from the cells, so there’s no cure for the condition. Each person with Down syndrome has a unique experience. It's hard to tell how much a baby with Down syndrome will be affected as a child or an adult.

People with Down syndrome usually have mild-moderate intellectual impairment. This often leads to learning difficulties and may include developmental delay with speech and language.

People with Down syndrome often share common physical features, such as:

• small head, ears and mouth
• upward slanting eyes
• low muscle tone
• irregular spacing between the toes

Physical conditions linked with Down syndrome can include:

• heart problems
• reduced hearing and vision
• digestive issues
• ear, nose or throat issues

Many of these issues can be treated. Frequent health checks can ensure that any problems are detected as early as possible.

In recent times, support for people with Down syndrome has improved, through:

• medical advancements
• progress in social science
• better health care
• better education
• more employment opportunities

Accessing support services, especially early in life, will help the child improve their physical and mental abilities and reach their full potential.

How do you screen for Down syndrome?

Screening tests are offered to all parents at different times during pregnancy. Screening tests can only indicate if your baby is at increased risk of having Down syndrome, they cannot diagnose Down syndrome. The tests can also screen for other chromosomal conditions.

Most people will have the combined first trimester screening. This involves a blood test and ultrasound. and is about 95% accurate. If you are unable to have this test during your first trimester or choose not to be tested, another blood test is available during your second trimester. This test identifies 85% to 90% of babies with a higher risk of Down syndrome.

A newer, more accurate option for screening is the NIPT (non-invasive prenatal testing). This involves a blood test after 10 weeks and is 99% accurate at identifying babies at high risk of Down syndrome. The main barrier to this test is cost. There is no Medicare rebate meaning the blood test may cost you $400 to $500.

If a screening test identifies a higher risk pregnancy, you will be offered a diagnostic test which can confirm a diagnosis. These tests include:

• chorionic villus sampling (tests the placental tissue)
• amniocentesis (tests the amniotic fluid; the fluid around your baby)

How is Down syndrome diagnosed after birth?

Even if your antenatal tests are normal or low risk, Down syndrome may be detected at birth or during early infancy. Down syndrome is usually suspected due to the physical characteristics described above. In this case a genetic test are performed on a small sample of the baby’s blood to confirm the diagnosis.

Where can I go for more information and advice?

Your doctor or midwife will be able to answer any questions about testing for Down syndrome during your pregnancy.

Down Syndrome Australia has information and services available to parents, including being able to speak to a parent of a child with Down syndrome.