Pre-implantation Genetic Diagnosis (PGD) is one of the most recent advancements in the field of Advanced Reproductive Technologies (ART). PGD is a cutting-edge set of diagnostic tests offered to couples undergoing in vitro fertilization (IVF) treatment to screen embryos for genetic diseases, disorders and chromosomal abnormalities before transfer.

A genetic disease or disorder is caused by a mutation in a gene in DNA. When a gene is damaged, it can mutate; mutations cause the gene to send the wrong message to the proteins in the body. What this means is that when a gene is damaged, defective or mutated, it stops working properly and all the cells in the body it talks to (sends messages to) will malfunction; the result is a genetic disease. Most genes come in pairs, one inherited from the mother and one from the father. Depending on the disease in question, when a child inherits the gene from one or both parents, the child is at risk for the disease.

When Do Doctors Recommend PGD?

PGD is recommended for couples where they or their family has a history of a specific genetic diseases like cystic fibrosis and tay sachs; in these cases the testing is offered so a couple learn which embryos are free of disease and select those embryos that would not suffer from the disease condition for transfer. In addition, PGD is often recommended to couples who have suffered the trauma of recurrent miscarriage, as well as those with unexplained nfertility, advancing maternal age, and/or cases of severe male factor infertility. In these latter cases, PGD may offer the potential of increasing the chance of successful pregnancy, and may offer a better chance of delivering a healthy baby.

How is PGD Done?

Pre-implantation genetic diagnosis is basically a diagnostic procedure to test very early human embryos for specific genetic diseases and disorders, or identify embryos with chromosome abnormalities before selection for transfer. The procedure is only available to couples undergoing IVF treatment because the testing involves removing (biopsy) of a single cell from an embryo that has grown to at least eight cells in number.

PGD relies on technology to remove one or two cells from an embryo so that the genetic material in the cell(s) can be analyzed. The method of removing the cell(s) (biopsy) is relatively straightforward, yet not an easy procedure. The embryo(s) being screened are at the pre-implantation stage where it may have between six and twelve cells total that are still distinct from each other. The best labs report significant damage rates of less than 2 percent.

Once the cell(s) is removed, it can then be tested with an ever-growing number of probes, stains, or genetic amplification procedures that provide very detailed and specific information about each embryo tested. These removed cells are analyzed in the a laboratory to determine which embryos are free of genetic abnormalities. Once the embryo biopsy is performed, the cells are immediately sent to a lab for analysis. In most cases, results are available within 24 hours.

The procedure can also be used to test the genetic material of an egg before it is fertilized. Maturing eggs extrude two small droplets as they divide and reduce their genetic material to half. These droplets are called polar bodies, and they can be extracted and analyzed. Obviously, if a lethal condition is found in the egg, then fertilization need not even be attempted, since the egg in no longer a candidate for creating a viable pregnancy.

What Diseases Can Be Tested For?

Current technology allows testing for a large number of genetic-based diseases and disorders, including, but not limited to:

Alpha-thalassemia Anemia
Glycogen Storage Diseases
Beta-thalassemia Anemia
Hemophilia
Canavan's Disease
Huntington's Disease
Cystic Fibrosis
Marfan's Syndrome
Charcot-Marie-Tooth Disease
Myotonic Dystrophy
Down's Syndrome
Neurofibromatosis
Duchenne Muscular Dystrophy
Polycystic Kidney Disease
Fanconi Anemia
Retinitis Pigmentosa
Fragile X Syndrome
Spinal Muscular Atrophy
Gaucher Disease
Tay Sachs Disease

At the present time, there are more than 100 diseases which PGD technology can test for.

It is important to remember that PGD is not usually done without good reason. The cost of the process and risk to the embryo must be outweighed by the potential benefits of obtaining the genetic testing information. At the present time, more than 100 diseases and disorders may be tested for with PGD technologies and probes for other severe diseases and disorders are being added to the list frequently as they are discovered. The rapidly advancing technology of full genome amplification and testing with “gene chips” can be expected to reveal new information and applications in the future. It should come as no surprise that the best labs are demonstrating the ability to improve pregnancy rates in older women and those with unexplained infertility.

When You May Want to Use PGD

PGD is recommended for couples and families with a history of a specific genetic disease to identify the absence or presence of specific genetic disorders. As a result, only those embryos free of genetic disease will be transferred during the transfer stage of your IVF cycle to increase the chance of conception and ultimately a healthy baby. It's important to remember that even when PDG is used, there's no guarantee you will get pregnant using this technique, but at least you can be certain that if you do, your baby will be born free of the disease that was screened for with PDG.

The main advantage of PGD is that it avoids selective pregnancy termination (abortion) as the method makes it highly likely that the baby will be free of the disease being tested. The technology to screen embryos for genetic disease is not without controversy, but for many it does offer significant benefit and is recommended for couples who have severe inherited genetic diseases within their family history or identified through their own genetic testing.