Preimplantation genetic screening (PGS) or Next-Generation Sequencing (NGS) is now frequently referred to as preimplantation genetic testing for aneuploidy. This test screens the embryo for chromosomal abnormalities. A chromosomally normal embryo will have 46 chromosomes. Any deviation from this number will likely result in failed implantation, miscarriage, or a viable chromosome syndrome-like Down syndrome.

Although this might sound alarming, chromosomal abnormalities are commonplace. Over a third of all embryos from a 30-year-old woman are detected to have a chromosomal abnormality. As women get older, this proportion rises to approximately 80% abnormal by the time a woman is 40. For this reason, women who try to get pregnant later in life may experience difficulties conceiving, an increased chance of miscarriage, and an increased chance of having a child with a chromosomal syndrome-like Down syndrome, compared to a younger woman. As a result, reproductive endocrinologists often recommend PGS to women in their late thirties or early forties.