A karyotype test is basically a test that analyzes your chromosomes. It tells you how many chromosomes a person has and looks at the structure of each chromosome individually. A karyotype can be performed on any tissue but most often it is done from a blood sample, a sample of amniotic fluid or a piece of placenta obtained through chorionic villi sampling. Karyotyping is a complex process that involves growing the cells, obtaining the chromosomes, staining the chromosomes, analyzing the chromosomes and reporting the results.
A karyotype test is a critical step in determining if someone has Down syndrome. People with Down syndrome have an extra number 21 chromosome. This extra number 21 chromosome can occur in three different ways - full trisomy 21, translocation Down syndrome and mosaic Down syndrome. Only a karyotype test can tell you which form of Down syndrome your child has and what the chance is to have another child with Down syndrome.