Pre-implantation genetic diagnosis (PGD) allows individuals and couples who are concerned about passing on a hereditary disease to screen eight cell embryos for specific disorders. After undergoing egg collection and fertilisation, the embryos are assessed and normal embryos only are selected for transfer to the uterus. Diagnosis before embarking on a pregnancy can often be preferable to medically invasive and emotionally demanding prenatal diagnostic techniques.
Some of the screening procedures require highly specialised facilities.