Preimplantation Genetic Diagnosis (PGD) can be used to select embryos of a particular sex. In most cases this is only done to avoid sex-specific diseases, but can also be done for family balancing. PGD is normally recommended for couples where one or both of the parents are a known carrier of a genetic disease (i.e. hemophilia or cystic fibrosis). PGD is usually performed after a woman's eggs have been harvested and fertilized by her partner's sperm, but before the eggs have been transferred back to her uterus. When the fertilized egg has reached between the four- and ten-cell development stage, one or two cells (known as blastomeres) are gently removed from each embryo using a microsurgery technique similar to that used in ICSI. The DNA from the removed blastomeres is then analyzed for genetic diseases or disorders.

If any chromosmal abnormalities indicative of disease are found, the results will be carefully explained to the potential parents. The parents then decide which embryos they wish to transfer. This is an important and sometimes difficult decision that has to be made in a short period of time on the day of transfer. We recommend, therefore, that patients and families undergoing PGD talk over the possible outcomes beforehand so that they have adequate time to think through all of the issues at hand.