Preimplantation Genetic Testing (PGT) involves several steps, starting with an in vitro fertilization (IVF) cycle to produce multiple embryos. After the eggs are fertilized with sperm in the laboratory and the embryos develop to a certain stage (typically day 3 or day 5 of growth), a small biopsy of cells is taken from each embryo. The biopsy can involve removing a single cell from a day-3 embryo (cleavage stage) or several cells from the trophectoderm of a day-5 blastocyst (blastocyst stage). The DNA from the biopsied cells of each embryo is then analyzed to determine if it carries any specific genetic or chromosomal abnormalities. There are different types of PGT:

• PGT-A (Preimplantation Genetic Testing for Aneuploidy): Screens the number of chromosomes in the embryo to identify if there is an abnormal number (gain or loss), such as trisomy 21 (Down syndrome).
• PGT-M (Preimplantation Genetic Testing for Monogenic/Single Gene Defects): Tests embryos for specific inherited disorders caused by mutations in a single gene, such as cystic fibrosis or Huntington's disease. This testing usually requires knowing the specific gene mutation present in the family.
• PGT-SR (Preimplantation Genetic Testing for Chromosomal Structural Rearrangements): Screens embryos for structural rearrangements in the chromosomes, such as translocations or inversions, which may not cause problems for the carrier parent but can lead to embryos with an unbalanced number of genes. The results of PGT testing typically take a few days to a week. During this time, the embryos are cryopreserved (frozen). Once the results are available, the embryos identified as genetically normal are selected for transfer to the mother's uterus in a subsequent frozen embryo transfer cycle. PGT can significantly increase the chances of successful pregnancy and reduce the risk of having a child with a known genetic disorder.