BIOLOGY 287 Chapter Notes -Down Syndrome, Epicanthic Fold, Muscle Tone
12 Oct 2014
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Causes: the child gets an extra chromosome 21 at the time of conception (resulting in a total of. The odds increase to about 1 in 350 by age 35, and about 1 in 100 by age 40. The levels of afp and three hormones called unconjugated control, human chorionic gonadotropin, and inhibin-a are measured in the sample. This test can be performed during the first trimester, between 8 and 12 weeks. Disadvantage is that it carries a slightly greater risk of miscarriage: amniocentesis, performed between 15 and 20 weeks of pregnancy, involves the removal of a small amount of amniotic fluid through a needle inserted in the abdomen. The cells can then be analyzed for the presence of chromosomal abnormalities. It carries a small risk of miscarriage and preterm labor: percutaneous umbilical blood sampling (pubs) usually performed after 20 weeks; uses a needle to retrieve sample blood from the umbilical cord.
