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Updated March 15, 2009

Definition: An amniocentesis is an optional test done during pregnancy to detect chromosome abnormalities in a fetus.

An amniocentesis, or amnio for short, is usually done between 15 to 20 weeks of pregnancy and involves using a narrow needle inserted into the mother's abdomen to remove a small sample of amniotic fluid from around the fetus. This amniotic fluid contains fetal skin cells that have been sloughed off. The fluid is sent to a cytogenetics laboratory for chromosome analysis either by FISH analysis or by karyotyping. Chromosome analysis will reveal if the fetus has Down syndrome. There is a small risk (less than one in 400) that an amniocentesis can cause a miscarriage.

Pronunciation: am knee oh sen tea sis
Also Known As: amnio
Common Misspellings: amniocenetesis
The amniocentesis was done at 16 weeks of pregnancy and revealed that the fetus had an extra number 21 chromosome and thus had Down syndrome.
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