Down Syndrome in Depth

Testing for Down Syndrome

Pregnant2Day previously gave an overview of what Down syndrome is, who is at risk, what prenatal tests are available and what to do when faced with a positive test result. (To read this overview, click here). In this article, we expound on the prenatal tests available and their associated risks.

Please bear in mind that our aim is merely to present you with facts that will help you navigate some of the emotionally charged decisions you have to make during your pregnancy. If the baby you are carrying is indeed diagnosed with Down syndrome, we encourage you to become as informed as possible and to discuss the matter with a medical practitioner you trust before making any decisions. It is also advisable to speak with other parents of Down syndrome children.

As discussed previously, there are two types of prenatal tests available to detect Down syndrome: screening tests and diagnostic tests. Screening tests, which are non-invasive, estimate the risk that a foetus has of having Down syndrome and various other genetic abnormalities. These results are factored in together with the mother’s age, with the risks increasing after the age of 35, and much more dramatically after the age of 45. Screening tests are not diagnostic and the one risk they do carry is that of false positives. Pregnancies identified as ‘high risk’ by screening tests become candidates for diagnostic testing.

A diagnostic test will tell whether the foetus actually has Down syndrome or several other conditions. Diagnostic tests involve sensitive procedures and therefore carry a risk to the foetus. The following table summarises the tests available, when they are commonly performed and their associated risks.

(Note, the most accurate method to determine the gestational age of a foetus, which contributes to risk factors and evaluation of screening tests, is through ultrasound not by the date of last menstruation.)

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TESTING FOR DOWN SYNDROME

SCREENING TESTS

Nuchal translucency screening

{module Nuchal translucency screening}

Triple screen

{module Triple screen}

Quadruple screen

{module Quadruple screen}

Expanded Alpha fetoprotein (AFP) screening

{module Expanded Alpha fetoprotein (AFP) screening}

Should your screening test results place you at high risk, always bear in mind that due to the number of variables at play, these results cannot be 100% conclusive and should only form a basis for deciding whether or not to undergo more tests. For a true diagnosis, it is essential to examine the chromosomes of the foetus – this involves diagnostic testing which carries a greater risk to the foetus. Genetic counselling will often precede diagnostic testing. There are several reasons why you may opt for diagnostic testing. These include making the decision to carry the child to term, wishing to investigate potential medical interventions, planning for and preparing the family for a child with special needs and locating support groups and other resources.

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DIAGNOSTIC TESTS

Amniocentesis

{module Amniocentesis}

Chorionic Villus Sampling (CVS)

{module Chorionic Villus Sampling (CVS)}

Percutaneous umbilical cord blood sampling (PUBS)

{module Percutaneous umbilical cord blood sampling (PUBS)}

For further informative reading about Down syndrome, visit the following sites or keep visiting www.pregnant2day.co.za for updates.

www.downsyndrome.org.za
www.downsed.org
www.ndss.org

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