PGT is most commonly used to determine if an embryo has the correct number of chromosomes (22 pairs of autosomal chromosomes plus 2 sex chromosomes, either XX female or XY male). These genetically normal embryos are called Euploid and are used for Embryo Transfer. Conversely, embryos that are missing or have extra chromosomal material are abnormal or Aneuploid and are generally not used for Embryo Transfer.
Another common type of genetic testing for embryos is used to identify specific genes that are in a family tree and are known to cause disease. There are hundreds of examples of disease states that result from defects of a single gene (eg., sickle cell anemia, muscular dystrophy, cystic fibrosis…). PGT-M requires that DNA probes, specific to the family gene, be prepared and tested prior to being used to identify the gene in embryos. The process to prepare and test a DNA probe may take weeks or months to complete, but will result in an ability to remove affected embryos and transfer only embryos with the normal gene. In this way, a disease may be eliminated in a family line.