Our Tests

Preimplantation Genetic Screening (PGS)

What is aneuploidy?

Chromosomes are the structures in our cells that carry our genetic information (genes). Typically, we have 46 chromosomes in each of our cells. The chromosomes come in pairs (23 pairs in total); one copy of each chromosome is inherited from the egg, and the other copy is inherited from the sperm. Cells/embryos with 46 chromosomes (i.e. the correct number) are called euploid. Aneuploidy is a term used to describe a difference in the number of chromosomes. If an egg or sperm is missing a chromosome or has an extra chromosome, this results in an embryo with an extra or missing chromosome, resulting in aneuploidy. The most commonly known example of aneuploidy is Down syndrome, which is caused by an extra copy of chromosome 21.

What are the benefits of PGS?

Preimplantation Genetic Screening (PGS) is a method used to identify aneuploid embryos in conjunction with an In Vitro Fertilization (IVF) cycle. PGS is currently the only way to determine if an embryo contains the normal number of chromosomes prior to pregnancy. PGS reduces the chance of failed implantation or an early miscarriage, or of having a child with a chromosome abnormality (which often causes birth defects and intellectual disabilities), and increases the chances of a healthy pregnancy after an IVF cycle.

Without PGS, embryos are selected for transfer based on their physical appearance and development. It is important to note, however, that an embryo's development is not always associated with its chromosomal content. Therefore, a well-developed embryo may be selected for transfer, but may not result in a pregnancy due to abnormal chromosomes. PGS can give your physician another way to select the best embryo(s) for transfer, in order to maximize the chances of having a successful IVF cycle.

Every couple is at risk of producing embryos with chromosomal abnormalities. This risk increases as a woman gets older, and is independent of medical or family history and ethnicity.

Most embryos with chromosomal abnormalities will fail to implant or will result in miscarriage. Therefore, the frequency of aneuploidy in IVF embryos is much higher than the number of babies born with chromosome abnormalities. For example, a 35-year-old woman has approximately a 1 in 204 (0.5%) risk of having a liveborn child with a chromosome problem. However, at the time of IVF for a 35-year-old woman, approximately 45% of embryos will be abnormal.

How does RGI perform PGS?

PGS is performed on embryo biopsy samples. Following an egg retrieval and fertilization, one or more cells are removed from a blastomere (day 3 embryo) or blastocyst (day 5/6 embryo). These biopsied cells are shipped to our lab for PGS analysis. PGS does not require the submission of any parental blood samples or work-up prior to testing.

PGS can be performed by two possible methods:

  • Next-Generation Sequencing (NGS)

    Next-Generation Sequencing (NGS) is a state-of-the-art technology which analyzes the number of all 24 chromosomes (pairs 1-22, X and Y). NGS is a method in which the DNA sequence of the embryo biopsies is directly analyzed. This is used primarily to identify if there are extra or missing copies of whole chromosomes. This testing may sometimes detect smaller pieces of duplicated or deleted chromosomal material.

    The optimal accuracy for this testing is 98%, when performed on a blastocyst (day 5/6) embryo biopsy.

  • Array Comparative Genomic Hybridization (aCGH)

    Array Comparative Genomic Hybridization (aCGH) is a technology which analyzes the number of all 24 chromosomes (pairs 1-22, X and Y). aCGH is a method in which the DNA of the embryo biopsies is compared to a normal control sample. This is used primarily to identify if there are extra or missing copies of whole chromosomes. This testing may sometimes detect smaller pieces of duplicated or deleted chromosomal material.

    The optimal accuracy for this testing is 98%, when performed on a blastocyst (day 5/6) embryo biopsy.