What is Embryo Preimplantation Genetic Testing (PGT) and What are the Benefits?
Preimplantation Genetic Testing (PGT) is the ability to screen for genetic abnormalities before an embryo is implanted through In-Vitro Fertilization (IVF). This type of testing is often recommended because it increases the chance of successfully implanting the best possible embryo (or embryos) for the production of a live birth with a healthy baby. It can also be an opportunity to choose the sex of your baby, if you wish.
Two common PGT tests are called Preimplantation Genetic Diagnosis (PGD) and Preimplantation Genetic Screening (PGS). Both tests require a biopsy be completed on day five or six of embryonic development, and they are performed to provide you with very different information.
While PGD will be able to predict the presence of specific diseases or disorders, PGS will look for a multitude of abnormalities at once. In other words, PGD seeks to identify and diagnose specific conditions, whereas PGS seeks only to improve chances at a live birth based on severe chromosomal abnormalities.
What is PGD and What Does It Look For?
PGD is a series of tests that are used to identify and diagnose potential chromosomal abnormalities in embryos before they’re ever transferred to a uterus. By finding chromosomal abnormalities during the early stages of embryonic development, the best embryos can be selected for implantation, so there’s a better chance at a healthy live birth.
After eggs are retrieved from the intended mother or egg donor and fertilized to create the embryo, a doctor will then remove one or more cells from the embryo on day five or six for closer examination. The test looks first at the number of chromosomes in the embryo. A typical human has 23 pairs of chromosomes for a total of 46. PGD will be able to determine if Down Syndrome (marked by the presence of one additional chromosome) or any other chromosomal abnormalities are present.
In total, PGD testing can identify more than 100 different genetic conditions including:
- Cystic Fibrosis
- Huntington’s Disease
- Tay Sachs
- Muscular Dystrophy
- Sickle Cell Anemia
- Spinal Muscular Atrophy
- Muscular Dystrophy
- Marfan’s Syndrome
PGD is not known to cause any increased likelihood of birth defects. Currently, the only known risks are potential damage to the embryo in the biopsy phase or a misdiagnosis, though both occurrences are believed to be rare.
What is PGS and What Does It Look For?
PGS looks specifically at chromosomal numbers. A typical, healthy embryo should have 46 pairs of chromosomes. This test will identify if there are fewer or greater chromosomes than what is considered ideal.
Abnormalities in chromosomal numbers can lead to failure to implant, increased odds of miscarriage, and genetic disorders including Downs Syndrome.
Can Both PGD and PGS Tests Be Done?
A commonly asked question is if your embryo is able to have both tests completed. The general answer is yes.
More than 95% of Growing Generations’ clients choose to do embryo testing. However, whether or not to do any testing or both PGD and PGS is always up to you and your fertility doctor. Just remember to always advocate strongly for yourself and ask questions if there is ever anything you don’t understand—and Growing Generations is always here to help if you need additional resources or advice.
Thank you to Dr. Guy Ringler of California Fertility Partners for helping us with this article on PGT.