Preimplantation genetic testing is a technique used to identify genetic defects in embryos created through in
vitro fertilization (IVF) before pregnancy. Preimplantation genetic diagnosis (PGD) refers specifically to when
one or both genetic parents has a known genetic abnormality and testing is performed on an embryo to determine if
it also carries a genetic abnormality. In contrast, preimplantation genetic screening (PGS) refers to techniques
where embryos from presumed chromosomally normal genetic parents are screened for aneuploidy.
Because only unaffected embryos are transferred to the uterus for implantation, preimplantation genetic testing
provides an alternative to current postconception diagnostic procedures (ie, amniocentesis or chorionic villus
sampling), which are frequently followed by the difficult decision of pregnancy termination if results are
unfavorable. PGD and PGS are presently the only options available for avoiding a high risk of having a child
affected with a genetic disease prior to implantation.