What is preimplantation genetic testing (PGT)?

Preimplantation genetic testing (PGT) is a procedure in the in vitro fertilization (IVF) process whereby embryos created through IVF are tested for chromosomal abnormalities and gene disorders before being placed into the uterus. The use of PGT among IVF patients in the U.S. has been steadily increasing in the past few years and is now utilized in around 40 – 50% of IVF procedures at AFCC.

What are the types of PGT?

• Preimplantation Genetic Testing for Aneuploidy (PGT-A): Aneuploidy (chromosomal abnormality) is a common cause of failed implantation and miscarriage. PGT-A analyzes for an abnormal number of chromosomes and abnormal structure. Examples of aneuploidy are a missing chromosome (monosomy) or possessing an extra one (trisomy). Selecting a chromosomally normal embryo for transfer helps improve the chances of a successful pregnancy.
• Preimplantation Genetic Testing for a Monogenic Disease (PGT-M): With PGT-M, specific gene mutations that one or both parents are known to carry can be identified and unaffected embryos can then be transferred, reducing the chance for severe genetic disease in the offspring. Examples of genes that can be tested by PGT-M are cystic fibrosis, sickle cell anemia, and muscular dystrophy.
• PGT for Chromosome Structural Rearrangement (PGT-SR): PGT-SR tests the embryos of patients who are known to have a chromosomal structural rearrangement, such as inversion or translocation. These patients are more at risk for producing embryos that don’t have the correct amount of chromosomal material, with affected embryos less likely to result in a live birth. Patients with chromosomal structural rearrangements often have repeated miscarriages.

How is PGT performed?

After eggs are retrieved and fertilized in the IVF lab (often after 5-7 days of development), an embryologist will perform an embryo biopsy by removing a few cells from the part of the embryo that will become the placenta. These cells are then sent to a specialty genetics lab for analysis.

What are the indications for performing PGT?

• Advanced Reproductive Age: Miscarriages and chromosomal abnormalities are more common the older the female partner is. PGT-A is often recommended for women older than 35 undergoing IVF. Studies demonstrate that PGT-A may decrease miscarriages and increase live birth rates for these women.
• Single Gene Defects: In couples affected by a single gene defect (e.g., cystic fibrosis, muscular dystrophy) or carriers of a genetic disease due to single gene abnormalities, PGT-M can identify embryos carrying this disease, which may result in a severe or deadly condition in the child, and their transfer can be avoided. If a severe disease is transmitted through the X or Y chromosome, selecting an unaffected gender will ensure that the child will be free of disease.
• Reducing Multiple Births: By selecting a single healthy embryo through PGT-A, individuals and couples can avoid transfer of multiple embryos, and consequently avoid multiple births that often result in prematurity and place the babies and mother at increased health risks.
• Reducing Recurrent Miscarriages: Selecting a normal embryo by PGT-A may decrease miscarriages in couples in whom miscarriages are due to chromosomal abnormalities.

Are there any concerns with PGT?

• The value of PGT-A as a universal screening test for ALL patients undergoing IVF has NOT been demonstrated
• PGT-A’s role in recurrent pregnancy loss and implantation failure is still unclear
• PGT-A results may be equivocal (i.e., the laboratory is unable to confidently report a result for an embryo biopsy sample), leading to decisions not to transfer embryos that may otherwise become healthy babies
• PGT-A is an additional expense and requires special expertise by lab personnel
• PGT-A results may be equivocal (i.e., the laboratory is unable to confidently report a result for an embryo biopsy sample), leading to decisions not to transfer embryos that may otherwise become healthy babies
• Embryos can be damaged during the biopsy process, though this risk is reduced by having experienced embryologists perform the procedure
• Even with current advanced technologies for PGT, the error rate may be as high as 2%

PGT-A represents a huge advancement in the field of reproductive endocrinology. If you’re interested in learning more about how it could help you on your fertility journey, speak with your care team or schedule a consultation at AFCC.

Key Sources: The Use of Preimplantation Genetic testing for Aneuploidy: A Committee Opinion (ASRM, May 2024); Preimplantation Genetic testing for Monogenic Disease (ASRM)