Preimplantation Genetic Testing (PGT) Preimplantation genetic testing (PGT) is a screening test that can be performed on embryos created via in vitro fertilization (IVF) or Intra Cytoplasmic Sperm Injection (ICSI) to genetically analyze the embryos prior to transfer. One of the most common reasons that an embryo transfer does not result in a pregnancy is due to abnormal embryo genetics. PGT can ensure that the embryo selected for transfer has the correct number of chromosomes, thereby reducing the chances for a failed IVF or ICSI cycles and reducing the chance of miscarriage. These genetic defects include a missing or an extra chromosome in the embryo (for example, Down syndrome), single gene disorders (like sickle cell anemia), or the rearrangement of genes, which can cause pregnancy loss and birth defects.
Who are good candidates for PGT? Women aged 37 years or older (due to higher risk of abnormal embryo genetics with normal reproductive aging), Women who have had multiple unsuccessful fertility treatments, Couples who are at risk of having a child affected with an inherited genetic disease, History of recurrent miscarriages due to chromosomal abnormalities. Some patients seek IVF or ICSI with PGT to reduce the chance of a specific genetic condition occurring in their children. This type of PGT is called preimplantation genetic testing for monogenic disorders (PGT-M). In some cases, the patient themselves may have a genetic condition such as neurofibromatosis type 1 or Marfan syndrome that could be passed on to their children. In other cases, both members of a couple may be carriers for a recessive genetic condition such as cystic fibrosis or sickle cell anemia, or the individual using their eggs may be a carrier for an X-linked condition such as Fragile X syndrome. HLA matching is also available for families with certain blood disorders who may wish for an embryo that could be an HLA match for a sibling or other family member.
Our physicians and genetic counselor work closely with such patients and an outside laboratory to design personalized testing for their embryos. The goal of PGT-M is to predict which embryos are free of the genetic condition for which they are at risk, allowing the physician to select those embryos for transfer. PGT-M can greatly reduce the risk of having an affected child prior to pregnancy.
Screening for chromosome abnormalities (PGT-A and PGT-SR): PGT can also evaluate an embryo’s chromosomes, the structures in every cell that contain our genes. It is not uncommon for embryos have random chromosome abnormalities such as missing or extra chromosomes, also known as aneuploidy. Embryos with aneuploidy are more likely to result in a miscarriage or failed IVF cycle. Less commonly, aneuploidy may result in the birth of a child with a chromosome condition such as Down syndrome (trisomy 21).
In a typical IVF cycle, embryos are chosen for transfer based on their appearance under the microscope, which is referred to as their grade. The embryo’s appearance can give us some indication of its potential to result in a successful pregnancy, but it is not perfect. Preimplantation genetic testing for aneuploidy (PGT-A) provides additional information about the reproductive potential of the embryos and may help select the best embryo for transfer. PGT-A is most often considered for patients who have had recurrent pregnancy losses (miscarriages), multiple unexplained failed IVF cycles, a prior pregnancy or child with certain chromosome abnormalities, or based on the age of the individual providing their eggs. While PGT-A can be performed for any IVF cycle, there are both benefits and limitations that should be carefully discussed with your physician to determine if PGT-A is right for you.
One final type of PGT called PGT-SR is for structural rearrangements. This type of PGT is performed when a patient or their partner has a rearrangement of their own chromosomes such as a translocation or inversion. A person with a structural rearrangement of their own chromosomes is at increased risk to produce embryos with missing or extra pieces of chromosomes. Embryos with missing or extra pieces of chromosomes are more likely to result in a miscarriage or a child with serious health issues. PGT-SR can help to reduce those risks.
In a typical IVF cycle, embryos are chosen for transfer based on their appearance under the microscope, which is referred to as their quality grade. The embryo’s appearance can give us some indication of its potential to result in a successful pregnancy, but it is not perfect. Preimplantation genetic testing for aneuploidy (PGT-A) provides additional information about the reproductive potential of the embryos and may help select the best embryo for transfer. PGT-A is most often considered for patient who have had recurrent pregnancy losses (miscarriages), multiple unexplained failed IVF cycles, a prior pregnancy or child with certain chromosome abnormalities, or based on the age of the individual providing their eggs. While PGT-A can be performed for any IVF cycle, there are both benefits and limitations that should be carefully discussed with your physician to determine if PGT-A is right for you.
Candidates for PGT-A include: Couples who have had a previous pregnancy with aneuploidy Women who have had two or more miscarriages Women who have experienced previously failed embryo implantation Women diagnosed with unexplained infertility Women older than age 35 Women who have undergone numerous unsuccessful fertility treatments How are PGT-A, PGT-SR and PGT-M performed on embryos during IVF? The two main steps to the three types of PGT are the same. The first step is an embryo biopsy. The second step is analysis of the biopsy by a laboratory to conduct genetic testing on DNA. In both forms of testing, the biopsy is at the blastocyst (day 5 or day 6 of embryo culture) stage of development. The blastocyst consists of two cell types, trophectoderm (TE) that allows the placenta to develop and the inner cell mass (ICM) that later develops into the baby. The biopsy removes 3-10 cells from the trophectoderm (pre-placenta) for laboratory testing for genetic disorders. The cells that are destined to make the baby are not disturbed. Results are usually available within 7-10 days following the biopsy. The blastocyst is frozen right after it is biopsied to wait for the results of testing and then is thawed and transferred to the woman in a subsequent cycle.
PGT risks: There are no documented health risks for children born after PGT testing beyond the normal health risks to mother and child through IVF. Handling of the embryo, its biopsy, freezing, and thawing results in a small risk of damage leading to an embryo that does not implant. Generally, around 5% of embryos evaluated by PGT are lost due to such damage. Another risk of PGT is inaccuracy in test findings, as the testing is not 100% accurate. For this reason, it is recommended that the patient undergo typical prenatal testing when she is pregnant, such as amniocentesis.