AART - Preimplantation Genetic Diagnosis

  • What is Preimplantation Genetic Screening (PGS)?

    View Dr. Megan Dufton’s presentation on Preimplantation Genetic Screening

    View Dr. Megan Dufton’s presentation on Preimplantation Genetic Screening for Chromosomal Translocations

    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:

    1. On average 30 to 60% of embryos created in an IVF cycle can be aneuploid, and the majority of these will fail to establish a pregnancy.
    2. The chance of having aneuploid embryos increases with maternal age.
    3. Chromosomal abnormality is the most common reason for miscarriage. Patients with recurrent pregnancy loss or patients who have unexplained failure to conceive likely have a higher rate of aneuploidy.
    4. Knowing the chromosome status of each embryo should improve the chance of getting pregnant with IVF. Transferring embryos that have the correct number of chromosomes should improve the chances of the embryo attaching to the lining of the uterus, establishing an ongoing pregnancy, and resulting in a normal live birth.

    PGS could be considered for patients who:

    • have experienced 2 or more miscarriages;
    • are of advanced maternal age;
    • have had numerous unsuccessful IVF cycles;
    • have had a previous pregnancy affected by a chromosomal abnormality; or
    • wish to ensure that only chromosomally normal embryos are transferred to the uterus.

    PGS can also be used to detect chromosomal imbalances for patients who carry chromosomal translocations.

  • What is Preimplantation Genetic Diagnosis (PGD)?

    View Dr. Megan Dufton’s presentation on Preimplantation Genetic Diagnosis

    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.