PGD/PGS

PGD/PGS is the use of molecular testing technology to evaluate embryos for chromosome or specific genetic abnormalities. There are different reasons why PGD/PGS may be performed at Advanced Fertility. A cell biopsy is taken from each day 5 “blastocycst” embryo for genetic analysis. This analysis indicates which embryos have a normal number of chromosomes and which are unaffected by the specific disease in question. Genetically normal embryos have a very high chance of leading to live birth. Advanced Fertility has been successfully performing embryo biopsy procedures since 2006 and the embryo screening technology is continually improving.

PGD– used for a “known” genetic disease such as Huntington’s disease.

PGS– used to screen for “possible” chromosomal disorders only. Not used for a specific gene. It can also be used for family balancing.

Reasons for using PGD/PGS

Embryos can be analyzed for one or more of the following reasons:

  • Aneuploidy- A condition in which there is an extra or missing chromosome. An example of aneuploidy is Down’s Syndrome. There is an increased incidence of aneuploidy as women age.
  • Translocations- A change in chromosome structure in which chromosomes are attached to each other or pieces of different chromosomes have been interchanged.
  • Single Gene Disorders- Disorders of diseases caused by the inheritance of a single mutated gene. Diseases include, but are not limited to, Cystic Fibrosis, Tay Sachs, Alpha and Beta Thalassemia, Sickle Cell Anemia and Huntington’s disease.
  • IVF Treatment Failure- one of the most common reasons why IVF doesn’t work is related to an abnormal chromosome number within the embryos. Patients with repetitive implantation failure or pregnancy loss may find answers with this approach.

Advanced Age & Aneuploidy
As a woman’s eggs age, the risk of chromosome abnormalities increases drastically. This causes a lower chance of pregnancy and a higher chance of a miscarriage. It has been known for many years that as a woman ages, her eggs are more prone to errors in cell division. These errors will cause the embryos to have too many or too few chromosomes making them genetically unbalanced. Most genetically unbalanced embryos do not lead to pregnancy. However, unbalanced embryos that do lead to pregnancy may result in a miscarriage or a baby with a chromosome disorder such as trisomy 21, or Down’s Syndrome. Blood testing in pregnancy (MSAFP or triple and quad marker screening) has been used along with ultrasounds and amniocentesis (drawing fluid from around the baby) to test for chromosome problems during midtrimester pregnancy. Chorionic villus sampling, which is a biopsy of tissue near the fetus, can be used to test a pregnancy after 8 weeks of pregnancy. However, preimplantation testing allows for screening for genetic problems before the embryo is placed into the uterus. This allows a patient to reduce the risk of having a pregnancy with a specific genetic problem or chromosomal unbalance. Embryos with diagnosed abnormalities are not transferred when PGD or PGS is used.

Translocations (unbalanced translocations & Robertsonian translocations)
Translocations are genetic abnormalities where the genetic material from one chromosome has relocated to another chromosome. The person with the abnormality possesses all of the genetic material they need but the genes are not in the normal places. A problem arises when the genetic material is passed on to the embryo. Missing or extra genetic information can be passed along. This can lead to genetic abnormalities or birth defects in the fetus. Preimplantation genetic diagnosis can determine which embryos do not show evidence of the translocation. This helps avoid miscarriages and increases the chances of a healthy baby.

Single Gene Disorders
There is a wide range of genetic diseases that can be evaluated using the genetic testing techniques. Current technology doesn’t offer a cost effective way to screen for all of the disorders at once. It is more effective to screen for a specific genetic disorder known within the family. Testing for single gene disorders is more complicated than the other tests and often has higher costs. A blood sample may be needed in advance so that the genetics center can create a probe to identify the genetic abnormality within the embryos tested. More information will be provided to you during your consultation if you desire single gene testing.