Preimplantation Genetic Screening (PGS) is genetic testing used in conjunction with in-vitro fertilization (IVF). PGS is used to detect aneuploidy by counting the number of chromosomes present in each embryo.
The DNA in our cells is stored in 23 pairs of chromosomes, for a total of 46 chromosomes. Our parents each contribute a set of chromosomes via the egg and the sperm.
We need this specific number of chromosomes for normal growth and development. Sometimes there are errors that occur in the number of chromosomes present in an egg or sperm, often for no apparent reason. Embryos from eggs or sperm with extra or missing chromosomes have a genetic imbalance, referred to as aneuploidy. Aneuploidy is responsible for the vast majority of spontaneous miscarriages, failed implantation, and can cause birth defects and intellectual disability.
The PGS results can help IVF physicians and patients decide which embryo(s) to transfer to the uterus.
PGS is a widely used procedure because:
PGS could be considered for patients who:
PGS can also be used to detect chromosomal imbalances for patients who carry chromosomal translocations.
Preimplantation Genetic Diagnosis (PGD) involves genetically testing embryos to identify a specific gene disorder (such as Cystic Fibrosis), so that unaffected embryos can be selected for transfer. Like PGS, PGD combines the technologies of IVF, embryo biopsy, genetic analysis, and cryopreservation.
Many common single gene disorders are inherited. Typically, genes are present in pairs, one from the mother and the other from the father. When the function of a gene is altered by a change in its specific sequence (a “mutation”), a genetic disease can result. These genetic mutations can be passed on in families from generation to generation.
The majority of genetic diseases are inherited in one of two different ways:
An autosomal dominant genetic disease is caused by a mutation in one copy of a gene; the risk for a parent with the disease to pass along that mutation to a child is 50%.
An autosomal recessive genetic disease is caused by a mutation in both copies of a gene, with a carrier having one normal copy of the gene and one copy with a mutation. The majority of carriers are healthy and are likely unaware that they are a carrier since having one normal copy is typically enough to prevent the disease. Two carrier parents have a 25% risk of having a child with the genetic disease.
If a genetic disease has been identified in your family, PGD can be used to significantly reduce the risk of the disease being passed to your offspring. Before starting your IVF cycle, a genetic test unique to your family will be designed, and genetic probes will be created to identify the specific single gene disorder identified in your family.
If you are interested in genetic testing, either PGS or PGD please inform our receptionists when you schedule your visit to the clinic.