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| Down syndrome | Features of Down syndrome Chromosomal abnormality Screening Tests for Down syndrome |
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Screening tests for Down syndrome | |
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| There are two types of
procedures available to pregnant women: screening tests
and diagnostic tests. Screening tests estimate the risk
of the fetus having Down syndrome; diagnostic tests tell
whether or not the fetus actually has the condition. The most commonly used screening tests are the Triple Screen and the Alpha-fetoprotein Plus. These tests measure quantities of various substances in the blood (alpha-fetoprotein, human chorionic gonadotropin and unconjugated estriol) and together with the woman's age, estimate her risk of having a child with Down syndrome. These screening tests are typically offered between fifteen and twenty weeks of gestation. Screening tests are of limited value and are often performed in conjunction with a detailed sonogram. These tests are only able to accurately detect about sixty percent of fetuses with Down syndrome. The procedures available for prenatal diagnosis of Down syndrome are chorionic villus sampling (CVS), amniocentesis and percutaneous umbilical blood sampling (PUBS). Each one of these procedures carries a small risk of miscarriage as tissue is extracted from the placenta or the umbilical cord to examine the fetus's chromosomes. The procedures are about 98 to 99 percent accurate in the detection of Down syndrome. |
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