Down syndrome screening tests from Feb 2010:

From 8 February 2010, new antenatal screening options for Down syndrome became available for pregnant women in New Zealand. These screening tests (combined blood test and nuchal translucency scan in first trimester, or blood test in second trimester) can show the likelihood of a fetus having Down syndrome or some other conditions. The screening tests do not give a definitive (final) result, but women whose screening results showed increased risk, will then be offered diagnostic tests, eg, chorionic villus sampling or amniocentesis.

The new screening tests should prevent some women from having to undergo the more invasive diagnostic tests, if their screening results show a low risk of Down syndrome and other conditions. Diagnostic tests (chorionic villus sampling or amniocentesis) can carry some risks to the fetus; the National Screening Unit reports there is a 1-2% chance of miscarriage from these procedures. Your doctor or maternity provider will discuss such risks with you before you choose to undertake a diagnostic procedure.

More about the screening tests is available from the National Screening Unit.

Diagnostic test - amniocentesis

Amniocentesis is a test that involves inserting a thin needle into a pregnant woman’s belly to take a sample of the fluid around the baby (amniotic fluid). It is possible to tell from the fluid whether a fetus has certain birth defects, especially what are called chromosome abnormalities. The fluid contains cells from the fetus, which are grown in the laboratory.

After careful processing the chromosomes in the cells are examined and counted. Chromosomes are the packages of all our genetic material, the blueprint for each of us. The correct number and arrangement of chromosomes are necessary for the development of a normal individual.

What does amniocentesis show?

The chromosomes in amniotic fluid can be used to diagnose chromosomal problems, such as Down syndrome (Trisomy 21), a mental and physical defect. Alpha-fetoprotein in amniotic fluid can also show whether a fetus has problems affecting the spine, lungs or other areas of the body.

Is it the right test for you?

Amniocentesis is a prenatal test that helps determine whether a fetus has health problems. The test is usually done between weeks 15 and 18 of pregnancy. In almost all cases the results are normal. Not every pregnant woman needs this test. Discuss with your lead maternity carer whether amniocentesis is right for you.

Should you have amniocentesis?

If the foetus has a higher than normal chance of birth defects or other problems, you may want to have this test. The following risk factors can increase chances of fetal health problems:

• you are aged 35 years or older
• there is a history of inherited (genetic) problems in your family
• other tests have shown the fetus may have health problems.

Amniocentesis can help determine if there is a problem. In very rare cases, amniocentesis can cause miscarriage. Your lead maternity carer will help you compare the benefits and risks of this test.

How is amniocentesis done?

First, the fetus is located using ultrasound (sound waves that make an image on a screen). A thin needle is then inserted into your belly. The doctor keeps the needle from touching the fetus by watching the screen. The needle is used to remove a small amount of fluid from your womb. Your body will make more fluid to replace what is taken. You can go home right after the test but you may need to take it easy for a day or so.

After amniocentesis

Call your doctor immediately if you notice:

• severe pain or cramping
• fever or chills
• vaginal bleeding (spotting)
• fluid leaking from your vagina.

Getting the test results

You will get your amniocentesis results in about two weeks. Most women’s results are normal. If yours are not, an obstetrician or a geneticist can help you and your lead maternity carer understand the results and arrange any special care you may need.

It's your choice

Ask your lead maternity carer any questions you have about amniocentesis. Having this
test is up to you. In New Zealand, it is offered to all women over 35 years old and others who may have had babies with abnormalities or a family history suggesting a risk of having a baby with chromosomal problems.

This information © 2001 The StayWell Company, 1100 Grundy Lane, San Bruno, CA USA 94066-3030 www.staywell.com (0800) 333-3032. All rights reserved. Original material reviewed by the Department of Maternal Fetal Medicine, National Women’s Hospital, Auckland. Updated by everybody, February 2010.