Comprehensive chromosomal screening (CCS) is performed on a few cells biopsied from a day 5 embryo called a blastocyst. The genetic material of the embryo is not altered in any way during CCS. During the time it takes to perform CCS, blastocysts are cryopreserved using a quick freezing method called vitrification. Embryo survival after vitrification is extremely high at 98%
