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GLOSSARY

Preimplantation genetic testing

Preimplantation genetic testing (PGT) examines embryos created using in vitro fertilization (IVF). PGT is used to diagnose genetically abnormal embryos or embryos that carry specific genes related to disease, before they are transferred into the patient's uterus. PGT helps avoid genetic defects at birth, miscarriage, and implantation failure and has since become an integral part of assisted reproductive technology.

What is preimplantation genetic testing?

Preimplantation genetic testing (PGT) is a genetic test performed on embryos created by in vitro fertilization (IVF). This testing screens embryos for abnormalities or genetic disorders, before implanting them in the uterus. The goal of PGT is typically to maximize the chances of creating a healthy pregnancy, or to avoid passing on genetic disease. It’s especially valuable when only one embryo is being implanted in the uterus.

Research indicates that embryo aneuploidy (extra or missing chromosomes) is the main cause of unsuccessful IVF cycles, as well as pregnancy loss. Abnormalities increase with rising maternal age, but can also be related to poor-quality sperm.

PGT is performed on a small sample of cells pulled from the embryo via needle biopsy. PGT may be done:

  • when the biological mother is 35 or older
  • when a patient has experienced at least two consecutive miscarriages
  • after previous unsuccessful implantations
  • when male-factor fertility is present
  • when one or both partners may transmit a genetic disease

Types of preimplantation genetic testing

There are several types of PGT that may be used depending on the risk factors present. Tests include:

  • Preimplantation genetic testing—aneuploidy or PGT-A. This test checks for the proper number of chromosomes (23 pairs, 46 total). AZn embryo with too few or too many chromosomes may not develop, leading to miscarriage, or may result in genetic disorders. PGT-A may be performed in cases of advanced parental age, history with miscarriage, or past failed IVF cycles.
  • Preimplantation genetic testing—monogenic or PGT-M. This test evaluates the embryo for specific genetic disorders that could be passed down from one or both parents, such as cystic fibrosis, Huntington’s disease, or hereditary cancer. This is performed when one or both parents is a known carrier of a gene, or if there’s a family history of a specific disorder.
  • Preimplantation genetic testing-structural rearrangements or PGT-SR. PGT-SR would be performed in cases when one of the biological parents has a known chromosomal abnormality. This analysis is used to determine whether the embryo has any missing or extra pieces on its chromosomes, as generally, embryos with such abnormalities do not result in successful pregnancies.

Preimplantation genetic testing and male-factor infertility

Chromosomal abnormalities in embryos can sometimes be caused by sperm. Studies show that genetically abnormal sperm, sperm DNA fragmentation (damaged sperm DNA), and Y chromosome microdeletions (genes missing from the Y chromosome, which is important for sperm production) can reduce embryo quality.

PGT may be performed if a patient:

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