Prenatal Screening and Testing for Down Syndrome



down syndrome testingThere are two ways of finding out if there may be Down syndrome in the fetus, through screening and diagnostic tests. A screening test will look at the risk factors the baby may have while the diagnostic test will give a definite answer to the question. Many women opt for screening because they are less expensive and less invasive. There are less risks of miscarriage with screenings than with diagnostics. The downside to a screening test is that it does not give a definite answer, just gives an indication. Generally, if a screening gives a positive indication, a diagnostic test can be done to determine if it is a false positive or a negative.

Diagnostic testing is not without severe risks. These tests invade the uterine cavity and the placenta and sac. This can lead to miscarriage, which will kill the baby or an infection from introducing foreign material into the sterile environment of the womb. But diagnostic testing can give an almost 100% definite answer to the presence of Down syndrome. Because of these risks though, diagnostic testing is normally only recommended for older mother, or for those who have genetic defects in their family history or if they received a positive on the screening test.

Screening Tests for Down Syndrome

An integrated screen is done when screening tests from the first and second trimester have been performed, and the results are compared and reevaluated. Sometimes the integrated screen is also done with a nuchal translucency. The nuchal translucency testing is done sometime during weeks 11 through 14 of the first trimester. This is done with an ultrasound that measures the folds on the back of the baby’s neck. This is because children with DS may build up fluid in this space causing it to be larger. The presence of a larger measurement does not mean the child has DS though. The results of such a screening should be read in conjunction with a blood test.

The multiple marker test is a blood test that takes a measure of certain substances in the mother’s blood. These tests are done in the second trimester between weeks 15 to 18. There are two types of market tests, a triple and a quadruple. The quad test is more accurate because it test for one additional marker. A level II ultrasound can be done at weeks 18 to 20 to look at the physical traits and check for abnormalities. Normally these tests are done together with the blood tests to arrive at a better indication of whether or not Down syndrome has been indicated.

Diagnostic Test for Down Syndrome

There are three such tests that are almost 100% accurate in finding out if the baby has Down syndrome or not. The tests are amniocentesis, chorionic villus sampling or CVS and PUBS (percutaneous umbilical blood sampling). These tests all have a risk of causing a miscarriage because they are very invasive. Each test needs a sample of either the umbilical cord blood, amniotic fluid or a piece of the placenta. When the sample is extracted, miscarriage and infection can occur. A patient needs to ask herself if these risks are worth it in the end.

 




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