 Some couples who undergo IVF also opt for preimplantation genetic diagnosis (PGD) whereby the genomes of their embryos are analyzed and particular embryos then selected for implantation. This is more common among couples at risk for transmitting a genetic disease or who are trying to create a child compatible with an existing ill child so that she can be used as a source of donated stem cells. However, it can be used for selecting for or against other traits, such as sex, or disability—for example, some deaf parents want to raise children who inherit their deafness. Such uses of PGD are controversial (on sex selection see Heyd 2003; Robertson 2003; Purdy 2007; ESHRE Task Force 2013; on selecting deafness see Karpin 2007; Fahmy 2011; Schroeder 2018).