Screening for Down syndrome

Down syndrome is a common genetic (chromosomal) condition causing mild to moderate intellectual disability. People with Down syndrome can also look different from other people and have some additional health issues.

Most people have 23 pairs of chromosomes in every cell in their body. People with Down syndrome have an extra chromosome 21. This is why Down syndrome is also known as Trisomy 21.

There are a range of antenatal tests offered during pregnancy to check the health of your baby.

Screening tests can be done to see if your baby has a high chance of being born with a chromosomal health condition such as Down syndrome.

Screening tests for Down syndrome involve ultrasound scans and blood tests.

A screening test cannot diagnose Down syndrome or tell you for certain that your baby has a genetic condition.

There is a small chance that any baby can be born with a genetic or chromosomal condition. Having a screening test early in your pregnancy will give you time to consider what it means.

Prenatal screening and diagnostic testing provide information about the health of your baby. This allows you and your family to make informed decisions such as:

• having extra monitoring during the pregnancy
• planning for how you will care for your baby
• opting to end the pregnancy

If screening shows that your baby is likely to have Down syndrome, you will be offered a further test to confirm this.

An early diagnosis of Down syndrome can help you and your doctor continue to check your baby for complications and to act early if needed.

Before you have the test it's a good idea to think about why you are choosing to do it, and how you will feel once you get the results.

Talk about your options with your doctor, midwife or a genetic counsellor.

Consider who you want to discuss any important decisions with — your partner, a friend or family member. Give yourself some time to make your decision.

Before going for the test ask your doctor or midwife if you need to do anything to get ready for the test.

There are 3 ways to have screening for Down syndrome:

1. combined first trimester screening
2. non-invasive prenatal testing
3. second trimester serum screening

Combined first trimester screening

The most common way to screen for Down syndrome is to have the combined first trimester screening. This involves having both:

• a blood test between week 10 and week 13 of your pregnancy
• a nuchal translucency ultrasound scan from week 11 to before week 14 of your pregnancy

The blood test measures levels of a protein that is made in your placenta called pregnancy-associated plasma protein A (PAPP-A). The blood test also measures the amount of a hormone called free beta human chorionic gonadotropin (free β-hCG).

Results from your blood test and nuchal translucency scan are combined to estimate the chance of your baby having Down syndrome. The risk calculation also uses factors including your age and weight.

The combined first trimester screening will pick up about 85% to 90% of babies that have Down syndrome.

Non-invasive prenatal testing

A newer option for screening is NIPT (non-invasive prenatal testing). This involves a blood test after 10 weeks of pregnancy.

NIPT is 99% accurate at identifying babies at high risk of Down syndrome.

The main downside to this test is the cost. An ultrasound is not needed with this test.

Second trimester serum screening

You might not be able to have the screening test for Down syndrome during your first trimester or choose not to be tested. In this case you can have a different blood test during your second trimester.

For this test, a blood sample is taken between week 14 and week 20 of your pregnancy.

The second trimester screening test measures proteins and hormones in your blood and can detect around 75% of babies with Down syndrome.

The combined first trimester blood test is covered by Medicare. But there may be costs for the ultrasound.

The NIPT blood test is not currently covered by Medicare or private health insurance. This test may cost you around $400 to $500.

Ask your doctor to explain the costs of each test. Find out if you can access free screening through the public hospital system.

Your doctor or midwife will be able to explain your results.

If your screening test shows a high chance that your baby has a condition such as Down syndrome, you will be offered a further test that can confirm the diagnosis.

You can also be referred for genetic counselling to help you work out how you feel about the results.

Your doctor can order a diagnostic test to find out whether your baby has Down syndrome.

Diagnostic tests include:

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

After your baby is born, a blood test may be done to confirm Down syndrome.

It's your choice whether to have these tests. Speak with your doctor or midwife to help you decide if screening for Down syndrome is right for you.

You will be given information about each test so that you can make an informed decision.

Questions for your midwife or doctor

Here are some questions you might want to ask your midwife or doctor:

• Why are you offering me this test?
• What does the test involve?
• Do I need to do anything on the day?
• When will I get the results?
• Who will contact me to give me the results?
• Do I need to do anything to care for myself after the test?

More questions to ask your doctor about tests and scans.

Down Syndrome Australia provides support, information and resources for people with Down syndrome and their families across Australia.

Support services include:

• information and advice about Down syndrome
• new parent packs
• workshops and webinars
• translated resources in Chinese, Arabic, Hindi and Vietnamese.

You can call 1300 881 935 to connect with your local state or territory Down syndrome organisation.

The best way to find a genetic counsellor is to ask your doctor to refer you to one.

The Human Genetics Society of Australasia also has a Find a Genetic Counsellor service. It can help you find a registered counsellor nearby.