Preimplantation genetic testing for aneuploidy (PGT-A):
This type of PGT screens embryos for certain chromosome abnormalities. Human embryos typically have 23 pairs of chromosomes (46 total) in each cell.  One chromosome in each pair is contributed by the egg, and the other is contributed by the sperm.  It is common for embryos to have random chromosome abnormalities such as a missing or extra chromosome, which is called aneuploidy.

In the majority of cases, these chromosome abnormalities happen by chance and are not inherited from a parent or donor.  Embryos with aneuploidy are more likely to result in miscarriage or a failed transfer.  Some types of aneuploidy may result in the birth of a baby with a chromosome condition such as Down syndrome or Turner syndrome.