This procedure involves removing a small number of cells from embryos to identify genetic defects. This technique gives us advantage to select embryos with normal chromosomes for implantation. Generally, we will remove embryo cell during cleavage (3 days growth) or blastocyst (5 days growth) to identify genetic defects by 2 ways; Pre-Implantation genetic diagnosis (PGD) refers specifically to check that couples with a risk of having heritable genetic diseases. In contrast, Pre-Implantation Genetic Screening (PGS) refers to techniques where embryos from presumed chromosomally normal genetic parents are screened for aneuploidy. In this case the couples have no heritable genetic diseases evident but still have a high risk of having a baby with chromosomal abnormality proven from a previous baby with chromosomal abnormality or age over 40 years old. PGS is also covering sex chromosome screening of embryo.
However, these techniques are just only identifying chromosomal abnormality not covering all other diseases or illness developing after implantation.