Anne Borkowski, MD

Reproductive Endocrinologist
Infertility Specialist

4250 Dempster St.
Skokie, IL, 60076
847-763-8850

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PGS, Preimplantation Genetic Screening

What are Single Gene Disorders?

Single gene disorders are genetic conditions caused by an alteration (mutation) in a specific gene. Single gene disorders are often hereditary (run in families), and therefore, individuals with a family history of a single gene disorder may be at risk for passing the condition onto their children. Examples of single gene disorders include cystic fibrosis, sickle-cell anemia, Tay-Sachs disease, Duchenne muscular dystrophy, Fragile X syndrome and spinal muscular atrophy (SMA).

What is PGD for Single Gene Disorders?

Preimplantation Genetic Diagnosis (PGD aka Preimplantation Genetic Testing for Monogenic Conditions) is used to identify embryos that are predicted to be affected with a genetic disease and those that are not. Currently, PGD is the only way to determine whether an embryo is predicted to be affected with a genetic condition prior to achieving pregnancy.

PGD has been utilized by many couples wishing to greatly reduce their risk of having a child with a genetic disorder as well as the possibility of being faced with a difficult decision about the outcome of a pregnancy following abnormal prenatal test results.

We can perform PGD for essentially any single gene disorder for which the mutation is known, including very rare conditions. 

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 PGT-A (aka PGS)?

Pre-implantation Genetic Screening (PGS aka Pre-implantation Genetic Testing for Aneuploidy) 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 live born child with a chromosome problem. However, at the time of IVF for a 35-year-old woman, approximately 45% of embryos will be abnormal.