For those people with recurrent pregnancy loss or infertility, PGS applies the technology from PGD to improve their chances for a successful pregnancy. Embryos are screened for aneuploidy (missing or additional numbers of chromosomes), which is a leading cause of miscarriage and implantation failure (failure of the embryo to implant into the uterus). The goal of PGS is to identify chromosomally abnormal embryos, so they will not be transferred leaving the chromosomally normal embryos to be transferred in the attempt to achieve a successful pregnancy.