Preimplantation Genetic Diagnosis (PGD) is a technique that can be used during in vitro fertilization (IVF) procedures to test pre-embryos for genetic disorders prior to their transfer to the uterus. PGD makes it possible for couples or individuals with serious inherited disorders to decrease the risk of having a child who is affected by the same problem. At present, PGD is only offered in approximately 10 centers in the United States including the Virginia IVF and Andrology Center.

PGD was first performed in 1989. It has since been successfully used to screen for a wide variety of genetic diseases, either single gene disorders or chromosomal abnormalities. In single gene disorders where the gene structure is known, such as cystic fibrosis or Tay-Sachs, the actual genes of the sampled pre-embryo can be examined for the presence of the condition. Other genetic conditions, such as Duchenne Muscular Dystrophy or hemophilia, affect only males. In these cases, while the exact gene defect may not be known, the DNA of the biopsied cell can be examined to determine the sex of the pre-embryo and only female pre-embryos replaced. Finally, in cases of severe recurrent chromosomal diseases, such as Down syndrome (which has an extra chromosome), the number and character of several chromosomes of the sampled pre-embryo can be determined.

Additionally, in couples who undergo multiple IVF procedures which fail to result in pregnancy, it is possible that chromosomal abnormalities are responsible for a significant percentage of implantation failures. The incidence of abnormalities may be increased for women of advanced reproductive age. PGD allows those couples the option to examine chromosomal health of their pre-embryos before transfer. The same is true for couples who achieve pregnancy, but suffer repeated miscarriages.

EXAMPLES OF COUPLES WHO MAY CHOOSE PGD

• One or both partners are carriers of single gene disorders, such as cystic fibrosis or Tay-Sachs disease.
• The woman is of advanced maternal age (> 38 years old), and is at risk for chromosomal aneuploidy such as Down Syndrome.
• The woman has a history of repeated spontaneous miscarriages.
• They have failed to conceive after multiple IVF attempts.
• One of them may have chromosomal translocations or other chromosomal abnormalities.

HOW IS PGD PERFORMED?

Pre-embryos are obtained by IVF in the laboratory, usually combined with ICSI. Once the pre-embryo(s) has been allowed to grow to approximately 3 days old, a single cell is removed from each pre-embryo under the microscope and the cell is sent to a specialty laboratory to analyze it for the presence of genetic disorders. A diagnosis is obtained within a day or so of the test, and only the pre-embryos showing no genetic defects are transferred to the woman's uterus.

For more information, please visit: American Society For Reproductive Medicine Reprogenetics