Preimplantation Genetic Diagnosis (PGD)
Preimplantation Genetic Diagnosis (PGD) is a test used to screen for specific genetic disorders in IVF embryos prior to transfer and subsequent implantation.
The first PGD baby was born in 1992. Both parents carried Cystic Fibrosis, a genetic condition where the body produces abnormally sticky mucus that can cause severe respiratory disease. For this family and so many others who would come after them, Preimplantation Genetic Diagnosis is the difference between passing on a life-threatening disease and giving their children the best chance at a healthy, happy future.
Since 1992, we have developed the ability to use PGD to test for a wide variety of genetic diseases including Tay-Sachs, Fragile X, Franconi Anemia, and many others.
To date, the international medical community has performed successful PGD testing that has in turn resulted in the births of more than 7,000 healthy babies.
The ability to diagnose and exclude embryos with verified genetic abnormalities prior to implantation and actual initiation of a pregnancy offers at-risk patients a way to prevent passing on inheritable genetic diseases before implantation.
PGD is also beneficial in that it offers alternatives to the clinical risks associated with chorionic villus sampling (CVS) or amniocentesis, two procedures that can only be performed once a pregnancy is in progress to check for genetic diseases.
Above all, it greatly reduces the possibility of discovering a serious genetic abnormality during pregnancy and subsequently facing the heart-wrenching decision of whether or not to carry the pregnancy to term.
When is PGD Indicated?
PGD testing is indicated when certain risk factors are present, including but not limited to:
- When there is a familial history of hereditary genetic disorders
- When chromosomal abnormalities are present in (or carried by) one or both partners
Couples already undergoing PGD to screen for chromosomal abnormalities may also decide to screen embryos for chromosome number, which includes the gender chromosomes. This is especially useful if family balancing is a secondary concern.
In the case of sex-linked genetic disorders, such as hemophilia or Duchenne Muscular Dystrophy, which generally affect only male children, PGD can be also be used for gender selection to choose only female embryos which will not be affected by the disorder.
Only embryos that are genetically normal are transferred into the patient’s uterus.
The PGD Procedure
The PGD process begins with egg retrieval and embryo culture as part of IVF. Once the retrieved egg has been fertilized in our laboratory, the embryo is allowed to develop for five days, at which time we biopsy three or four cells from what is now the trophectoderm, a layer of cells that will eventually become your baby’s placenta.
Under a high-power microscope and with the use of sophisticated, hydraulically-operated, ultrafine microscopic glass instruments, the Fertility Institute’s experienced embryology team stabilizes the embryo and makes a small hole in the shell surrounding the embryo.
This state-of-the-art technique, called “assisted hatching,” involves using a special laser to assist the embryo’s natural hatching process, creating a small window through which the cells emerge.
The small sample is then quickly microsurgically shaved off without significantly affecting the embryo and sent off for analysis.
The embryo is then frozen using vitrification, an ultra-rapid and safe freezing technique, and is paused in its development while the PGD testing takes place. When the results are received (usually in 7-10 business days), they will be discussed with the patient, and a frozen embryo transfer (FET) is scheduled. During the FET cycle, only a normal embryo or embryos are transferred into the woman’s uterus.
Preimplantation Genetic Diagnosis (PGD) vs. Preimplantation Genetic Screening (PGS)
Basically, PGD is most commonly used when a couple is looking to diagnose or screen for a specific genetic disease, such as when the parents are carriers of Tay-Sachs disease, cystic fibrosis, or another single-gene mutation, or are carriers of a balanced translocation.
PGS, on the other hand, is a more generalized test in which the embryo is screened not for a specific genetic disease but rather for general chromosome number abnormalities (or aneuploidy.) Abnormalities in chromosome number can lead to failed IVF cycles, miscarriages, and/or birth defects. Many people use PGS and PGD interchangeably.