Down syndrome screening tests 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.

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

Early screening of fetal health - AFP test

When you are pregnant, substances from your fetus mix with your own blood. A blood sample taken from your arm can be used to find those substances. An alpha-fetoprotein (AFP) test is a simple blood test. It can show whether your fetus has signs of some birth defects, in particular, spina bifida (a type of neural tube defect).

The test is done between weeks 14 and 18 of pregnancy. In New Zealand this test is part of the Maternal Serum Screening programme and is not used on its own to screen for neural tube defects.

Understanding AFP tests

An AFP test is only a screening test. The most it can do is point to a possible problem. If the results of an AFP test point to a problem, other tests will be needed to confirm the results. Bear in mind that most AFP test results are normal. Even when they are not, the results of the follow-up tests most often are.

AFP test results

Once a blood sample has been taken by your lead maternity carer you will get your AFP test results within two weeks. When done as part of the Maternal Serum Screening programme, the test takes around 10 days for a result. The test is performed at the National Testing Centre at Auckland Hospital. The results may show the presence of certain fetal substances in your blood and can alert your lead maternity carer to possible birth defects.

Most AFP results are negative (normal). This means the test results show no signs of the birth defects tested for. Sometimes results are positive (abnormal). Often, this is simply because:

• your due date is different than first thought
• you have twins.

Some positive results show that the fetus may have one of the following birth defects:

• neural tube defects (problems with the spine, such as spina bifida)
• abdominal wall defects (problems with the body of the fetus)
• genetic defects (physical or mental problems, such as Down syndrome).

Rarely, AFP test results can be wrong. These are called false negatives or false positives. Be sure to ask your lead maternity carer any questions you have about your results.

Other tests

If your test results are positive, you may undergo more tests. These additional tests can confirm whether there really is a problem or whether everything is normal. The tests include:

• ultrasound - this uses sound waves to create an image of the fetus
• recalculated AFP - a second AFP test, used if ultrasound shows that your due date is different than first thought or that you have twins
• amniocentesis - this is a test of the fluid that surrounds the fetus in the womb.

If these tests show no cause for concern, your lead maternity carer may still want to watch your pregnancy carefully. That way, any problems can be spotted early.

Should you have an AFP test?

Having an AFP test is up to you and like all screening tests is optional. Currently, the Maternal Serum Screening tests cost $75.00. An AFP test can warn you about some fetal birth defects. Here are some more facts to help you decide if you want to have it:

• an AFP test causes no health risk to you or the fetus
• an AFP test can only point to possible problems with the fetus
• if the test points to a possible problem, other tests will be needed to confirm the AFP results
• even AFP test results that are normal cannot tell for sure that the fetus is healthy.

What next?

The AFP test is just one of many you may have while pregnant. Most women’s AFP test results are normal. Even if they are not, the chances are high that the fetus is healthy. Ask your lead maternity provider any questions you have about this or the other tests.

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