Through preimplantation genetic diagnosis, it is possible to obtain genetic information about an in vitro embryo prior to its being implanted in the uterus. The genetic selection of embryos to be transferred to the uterus provides the means to increase the likelihood of pregnancy or to avoid the transmission of a known disorder. There are several reasons to resort to PGD technology however the main reasons are:

Single Gene Disorders
Testing for single gene disorders is probably the most frequent indication for PGD. In this case, it is performed to avoid the transmission of a disorder involving a single gene from carrier or affected parents where transmission of the gene could jeopardize the quality of life of the unborn child (e.g.: cystic fibrosis, myotonic muscular dystrophy Steinert disease, Huntington's chorea, Duchesne muscular dystrophy, etc.).

Aneuploidy Testing
In certain cases, testing for aneuploidy (abnormalities most frequently detected at birth, e.g.: trisomy 21, trisomy 18, Turner's syndrome, etc.) may be indicated. In this case, the aim is to optimize the likelihood of pregnancy by selecting embryos that are not carriers of aneuploidy. This method could be very helpful in cases where couples are suspected of having a high rate of chromosomal abnormalities (advanced maternal age, repeat miscarriages, repeat implantation failures, etc.).

What does PGD involve?
Because PGD is performed at the preimplantation stage, in vitro fertilization is required to obtain embryos. For technical reasons, in the case of single gene disorders,in vitro fertilization with sperm microinjection (ICSI) is required.

On day 3 of embryo development, when the embryo has reached the 8 cell stage, an embryo biopsy is performed by removing one cell. Genetic testing will then be performed on that cell. Pending test results, the embryo is returned to culture.

As a rule, test results are available on day 5. Once the diagnosis for each of the embryos is in, all that remains is to select one or more embryos for transfer.