This involves running a genetic test on the embryo to check for genetic anomalies. With the help of a laser, a few cells are removed from the embryo (embryo biopsy) which are subjected to genetic testing. In PGS (Preimplantation Genetic Screening) aneuploidy screening is done to look for numerical abnormalities in all 23 chromosomes; whereas in PGD (Preimplantation Genetic Diagnosis), testing is done for specific diseases which may be present in one or both partners in manifest or carrier form. In the meanwhile, the embryos are frozen, and only embryos which are normal are later transferred into the uterus.