What is Preimplantation Genetic Screening or PGS?

Preimplantation genetic screening (PGS) is a genetic testing procedure performed on embryos created with in-vitro fertilization by examining the chromosomes of an embryo for net gain or loss of genetic materials. Specifically PGS can identify chromosomal abnormalities such as

• Incorrect number of chromosome or aneuploidy – Aneuploidy is the presence of an abnormal number of chromosomes in a cell, such as having 45 or 47 chromosomes when 46 is expected in human cell. Examples of aneuploidy are:
  • Down Syndrome with an extra copy of chromosome 21,
  • Edwards Syndrome with an extra copy of chromosome 18.
• Translocation or rearrangement of one segment of chromosome onto another chromosome,
• Deletion or missing a segment of chromosome, or
• Sex-chromosome abnormalities including duplication or deletion of X and Y chromosome.
  Examples of sex-chromosome abnormalities include
  • Klinefelter Syndrome with three copies sex chromosome, two X and one Y
  • Turner Syndrome with only one copy of sex chromosome, one X

Who should consider PGS?

Because PGS screens embryos for chromosomal abnormalities, it identifies an embryo with normal chromosomal makeup with much greater precision than visual microscopic observation typically used in IVF. Hence PGS allows the selection of a normal embryo to be transferred and increase the likelihood of delivering a healthy baby.

Couples or individuals at increased risk for having embryos with abnormal chromosomes are best candidates for PGS. These include:

• Advanced maternal age (age 35 and older),
• Recurrent miscarriages, or
• Previous failed IVF attempt(s)

Other appropriate candidates for PGS are individuals or couples who desire

• Single embryo transfer to avoid multiple gestation,
• A desire to maximize the possibility of a healthy baby with IVF, or
• Family balancing

Does PGS test for a specific genetic disease?

PGS test for chromosomal abnormalities only. Preimplantation genetic diagnosis or PGD tests for single gene mutations associated with genetically inherited disease, e.g. cystic fibrosis, sickle cell anemia, muscular dystrophy, Huntington’s Disease, Fragile X syndrome and many more.

What are the risks of PGS?

Most of the risks involved in PGS treatment are similar to those for conventional IVF. For more information on the risk of IVF,

With PGS, there is also the possibility that:

• some embryos may be damaged by the process of cell removal,
• no or inconclusive result due to technical issues, or
• incorrect result because of chromosomal mosaicism in the embryo.

What is the Chance of Having a Baby with PGS?

The chance of a successful outcome with PGS in conjunction with IVF treatment depends on whether any and how many of the embryos produced in an IVF cycle have a normal PGS result. Current data report a live birth rate between high 60% to 80% when an elective single frozen embryo is transferred in a subsequent cycle. These data are very encouraging as most women undergo PGS and IVF are at higher risk of producing chromosomally abnormal embryos such as advanced maternal age, previous IVF failures or recurrent pregnancy losses.

Sometimes, however, no embryos are suitable for transfer to the womb, for reasons including:

• Not enough eggs are produced or fertilized,
• Removing the cells to be analyzed damages the embryos, or
• All the embryos are aneuploid.