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...irs, the fertilized egg will contain 47 pairs of chromosomes instead of the normal 46 pairs. The 47th pair is a third copy of the chromosome. In Down Syndrome, that copy is for chromosome 21. This is called trisomy. 95% of the births of children with Down Syndrome result from non-disjunction. Translocation can also cause Down Syndrome. In translocation, one part of a chromosome is stuck to a different chromosome. The chromosome 21 doesnˇ¦t stay separate; it breaks off and attaches to another chromosome, usually 14. There are a few different tests that can be done to find out if a child will be born with Down Syndrome. A screening test can estimate the risk of having a child with Down Syndrome. A diagnostic test can test the fetus to see if it has Down Syndrome. Karyotyping can be done after the child is born. They sample a little bit of the baby’s blood to confirm Down Syndrome. The triple screen and the alpha-fetoprotein, two types of blood tests, are two of the most common screening tests. These are usually given before week 20 and after week 15. Although these aren’t the most accurate procedures. Three of the diagnostic tests, chorionic villus sampling (CVS), amniocentesis, and percutaneous umbilical blood sampling (PUBS), are more accurate, about 99%. These tests are also a risk because it carries a chance of miscarriage. The procedure involves sticking a needle in the umbilical cord. CVS and amniocentesis can be given from weeks 8 to 20, while...