PGS requires an IVF be performed. Eggs are taken from the patient, identified by an expert and experienced embryologist and placed into an incubator. The eggs are fertilized with sperm the same day by conventional insemination or by Intracytoplasmic Sperm Injection (ICSI). The eggs are checked on a daily basis to document fertilization and growth.

After fertilization, an embryologist will take a few cells from the embryo for genetic testing. It will examine these cells for its gender chromosomes (XX for a female or XY for male) and/or for genetic defects. PGD can detect abnormalities of chromosome numbers, such as Down syndrome. It can also identify other serious single-gene disorders such as cystic fibrosis and sickle-cell anemia prior to embryo transfer. An abnormal number of chromosomes in the embryo (either too many, or too few) will likely cause failed implantation or miscarriage. The likelihood of having an abnormal chromosomal content increases with age.