How do you know?

I am constantly asked...How did you find out Mason had DownSyndrome...

After Mason was born they did a F I S H test.

to determine if there are three copies of the 21st chromosome which is done by fluorescence in situ hybridization (FISH). This is a very specific test and will only look for specific genetic differences. Examples are FISH for Trisomy 21, 18, or 13. There are several other FISH tests, but your child would only have the one for trisomy 21 at first.  

Maon has mosaic trisomy, the misdivision occurs after fertilization at some point during early cell division. Because of this, people with mosaic Down syndrome have two cell lines -- one with the normal number of chromosomes, and one with an extra number 21

Mosaic Down syndrome do not have the extra chromosome on every cell. They have a "mosaic" of affected and uneffected cells.

Children with Mosaic Down syndrome may have higher IQs than those with Down syndrome, but many of the health and development issues are the same.