PGT-A and IVF: What It Is, How It Works, and Who May Benefit
If you’re considering IVF, you’ve probably heard your fertility specialist mention PGT-A, or Preimplantation Genetic Testing for Aneuploidy. One of the most common questions I hear is:
“Should I have my embryos genetically tested?”
The answer depends on your individual situation. PGT-A is an important tool in modern fertility care, but it’s not the right choice for every patient. Understanding what it does—and what it doesn’t do—can help you make an informed decision.
What is PGT-A?
PGT-A is a genetic screening test performed on embryos created through in vitro fertilization (IVF). Its purpose is to identify embryos with the normal number of chromosomes before they are transferred into the uterus.
Humans normally have 46 chromosomes, arranged into 23 pairs. We inherit half from the egg and half from the sperm. Chromosomes contain our DNA and carry the genetic instructions needed for normal growth and development.
An embryo with the correct number of chromosomes is called euploid. An embryo with extra or missing chromosomes is called aneuploid.
Chromosomal abnormalities are the most common genetic abnormality found in human embryos and are a leading cause of failed implantation, miscarriage, and certain chromosome disorders, such as Down syndrome.
Why do chromosome abnormalities happen?
Most chromosome abnormalities occur by chance when eggs or sperm are formed. Although either parent can contribute, the majority originate from the egg, making maternal age the single biggest factor affecting embryo chromosome health.
As women age, the percentage of chromosomally normal embryos decreases.
Approximate rates of embryo aneuploidy are:
- Under 35 years: 25–40%
- 35–37 years: 40–50%
- 38–40 years: 50–70%
- 41–42 years: 70–80%
- Over 42 years: More than 80%
This is one of the primary reasons fertility declines and miscarriage rates increase with age.
It’s important to remember that PGT-A does not improve embryo quality. Instead, it helps identify which embryos already have the highest chance of resulting in a healthy pregnancy.
How is PGT-A performed?
Embryos are grown in the IVF laboratory for five to seven days until they reach the blastocyst stage.
At that point, an embryologist carefully removes approximately 5–10 cells from the embryo’s outer layer, called the trophectoderm. These cells will eventually form the placenta—not the baby itself.
The embryo is then frozen while the biopsy sample is sent to a specialized genetics laboratory. Using advanced technologies such as Next Generation Sequencing (NGS), the laboratory evaluates whether the embryo has the expected number of chromosomes.
Understanding the Results
Most embryos are reported as one of three categories:
Euploid: The embryo has the expected number of chromosomes and generally has the highest chance of implantation and live birth.
Aneuploid: The embryo has an abnormal number of chromosomes and is much less likely to result in a healthy pregnancy.
Mosaic: The embryo contains a mixture of normal and abnormal cells. Some mosaic embryos can still result in healthy pregnancies, but decisions regarding transfer require individualized counseling.
Who may benefit from PGT-A?
PGT-A is not recommended for everyone undergoing IVF. However, it may be particularly helpful for patients with:
- Advanced maternal age
- Recurrent pregnancy loss
- Multiple failed IVF cycles
- A previous pregnancy affected by a chromosome abnormality
- Multiple embryos available for selection
- A desire to reduce unsuccessful embryo transfers
The decision should always be individualized after discussing your medical history and reproductive goals with your fertility specialist.
Coming Next
In Part 2, we’ll discuss what the latest research says about PGT-A, review the current ASRM guidelines, explain its limitations, and answer one of the most common questions patients ask: Does PGT-A guarantee a healthy pregnancy?