Preimplantation Genetic Testing
Preimplantation genetic testing refers to the genetic testing of embryos prior to when they are placed in the uterus. Both PGD/PGS involve the same technique for the removal of a cell from an embryo that was created using In vitro fertilization (IVF). This testing is performed in order to determine if certain genetic anomalies are present in the embryo such as genes for diseases (PGD) or abnormal chromosome number known as aneuploidy (PGS). PGD/PGS is performed before embryo transfer during IVF so that doctors may pick one without a known or suspected gene problem (PGD), or one without an abnormal number of chromosomes (PGS). The goal of both PGS and PGD is to increase the chance of selecting a healthy embryo that will develop into a healthy baby. These advances can make a real difference as birth defects occur in nearly one in 20 pregnancies, ranging in severity from minor anatomic abnormalities to extensive genetic disorders, including mental retardation.
PGD: Preimplantation Genetic Diagnosis
Preimplantation Genetic Diagnosis, or PGD, is a diagnostic procedure in which embryos are tested for genetic abnormalities. Screening for a genetic illness can be done by performing PGD for a single gene mutation. In this situation, the embryos are screened not for a chromosomal problem, but for a single gene abnormality associated with a single disease. Thousands of gene loci have been identified. Certain illnesses are carried as traits by parents. When both traits are passed on to a child, she or he can be affected. Yet, for many such illnesses, carrier status can be diagnosed prior to conception. Both family history and ethnic background help to determine which testing may be appropriate for you. PGD screenings for single gene defects have been carried out for scores of genetic illnesses, including: cystic fibrosis, Huntington’s chorea, Marfan syndrome, Tay-Sachs and Sickle Cell Anemia.
PGS: Preimplantation Genetic Screening
PGS, Preimplantation Genetic Screening is when embryos are tested for chromosomal abnormalities. Chromosomes are sub-cellular structures that house one’s genes. All of the information that is needed to lead to an individual’s development is contained on these chromosomes and each one of us has 23 pairs of them. During human reproduction, it is not unusual to produce embryos that have too few or too many chromosomes, this is known as “aneuploidy”. PGS, also commonly referred to as Aneuploidy Screening is used to screen for commonly encountered embryonic chromosomal disorders. Infertile couples may benefit from this test if the female partner is older, if they have had several failed IVF cycles, or if they suffer from repetitive older miscarriages.
How to Determine if You Need PGD/PGS Testing?
The physicians of PFC have long-term experience as they are some of the first in the field to utilize this technology. At PFC, we perform PGD and PGS as indicated:
- Patients with in-born errors of metabolism (i.e. Tay-Sachs, Gaucher’s)
- Patients that carry genetic markers for known diseases (i.e. cystic fibrosis, hemophilia, sickle cell anemia, muscular dystrophy, etc.)
- Patients with unexplained miscarriages (over 60% of repetitive miscarriages are due to aneuploidy)
- Embryo screening to de-select aneuploidy electively
- Gender identification prior to embryo transfer electively
Can PGD/PGS Help Improve IVF Success Rates?
This is a controversial issue as patient selection (age, indication) does determine its efficacy. PGS or PGD can cause a transient stunting to the growth of the embryo and may decrease the overall pregnancy rate in young patients (less than 35 years of age) who would otherwise not need this procedure. For this reason, PGD/PGS screening(s) are not routinely done unless there is a history of repetitive pregnancy loss (miscarriages) in the younger patients or a medical indication for PGD. For all patients with RPL, regardless of age, this can increase the chances of a live birth.
PGD is done for genetic disease removal from the embryo so the resultant child will not be afflicted, and therefore is indicated when the goal is to do so. Older patients with increased risk of aneuploidy may benefit from PGS as well. Your physicians at PFC are experienced with this and fully understand the complexities and value of PGD/PGS. We will make sure you are informed completely to allow you to make the best decision in your management.
