Aneuploidy refers to an abnormal number of chromosomes and occurs during cell division as a result of improper chromosome separations between the cells. The condition can result in an extra or missing chromosome and is a common cause of genetic or birth disorders. Typically, chromosome abnormalities occur in 1 out of 160 live births. The most common abnormalities among these live births are the result of an extra chromosome in chromosomes 21, 18, and 13.
Trisomy refers to the presence of three copies of a particular chromosome instead of the normal two copies. An extra copy in chromosome 21, 18 and 13 is called Down syndrome (trisomy 21), Edwards Syndrome (trisomy 18), and Patau Syndrome (trisomy 13), respectively.