How do you detect down syndrome?

If you test for it in pregnancy the test is called a CVS or an Amniocentesis. They test the amniotic fluid or a piece of the babys' placenta for the third 21st chromosome.

After birth, they take some blood from the baby and run what is called a Karyotype. That test will count the chromosomes in the cells of the blood and if there are 3 21st chromosomes that means Down Syndrome