The expanding world of genetic testing for your embryos

A rundown of established and emerging technologies

This article walks through what we can (and can’t) learn from genetic testing of embryos. It reviews the different types of testing available today, from commonly used tools that look at chromosome number to newer technologies like genome sequencing. The goal? To help you understand the options, so you can make informed decisions with your care team.

What is preimplantation genetic testing (PGT)?

Testing performed on embryos before implantation, to gather genetic information that can guide embryo selection during IVF.

How is it performed?

After your egg retrieval, the medical team fertilizes your eggs with sperm in order to create embryos. They allow these embryos to grow for 5-6 (sometimes 7) days. At that point, the embryologist biopsies a few cells from the outer layer of the embryo (which later becomes the placenta, not the baby). These cells are sent for genetic testing, and that’s where your options begin.

Is it safe?

Embryo biopsy is considered a low-risk procedure when performed by experienced professionals.

Why?

• The biopsy is quite small. It’s only around 5-cells (out of hundreds!)

• Only the outer layer of the embryo is biopsied (not the part that becomes the fetus).

In fact… for many, PGT improves the chance of IVF success. However, no medical procedure is 0% risk, so always discuss the statistics with your specific IVF clinic.

Types of PGT

Note: PGT (of all types) is never a requirement; just an option.

PGT-A: Aneuploidy

“Aneuploidy” means abnormal number of chromosomes.

• PGT-A is the most common form of PGT; it’s essentially the default.

• It examines the chromosomes to determine if there are any extra or missing whole (or large pieces) of chromosomes.

• Most people have 46 chromosomes (23 pairs), including two sex chromosomes (XX in females or XY in males).

• When an embryo has a different number of chromosomes than the expected 46, it’s significantly less likely to result in a healthy pregnancy. (These embryos are either incompatible with life or associated with genetic conditions).

• So…transferring a chromosomally normal (aka "euploid") embryo improves your odds of success.

PGT-M: Monogenic disorders

This type of PGT is highly targeted. It’s used when there's a known genetic condition or risk in the family.

It’s available in the following settings:

• Carrier screening revealed high-risk results. Either you and your partner are carriers of the same recessive condition (e.g., cystic fibrosis), or the female partner is a carrier for an X-linked condition (e.g., Fragile X syndrome).

• One of you is affected with a dominant condition like Huntington’s disease or Marfan syndrome.

• There’s a known hereditary cancer (or other medical) risk. An example is a pathogenic variant in BRCA1 or BRCA2, which is known to be associated with high risk for breast, ovarian, and other cancers.

PGT-M essentially looks for the presence or absence of known familial variants in your embryos, and allows you to select an unaffected embryo if available.

PGT-SR: Structural rearrangements

• Some people have all the right genetic material, but parts of it are in the wrong place. For example, a chunk of one chromosome might be swapped with another (called a translocation) or flipped around (inversion).

• These rearrangements usually don’t affect your own health, but they increase risk for miscarriage or having a child with a genetic condition.

• PGT-SR detects abnormalities in chromosome structure and imbalances of genetic material, so a healthy embryo can be selected for individuals at risk.

Can more than one of these technologies be performed on a single embryo?

Yes. PGT-A can be combined with PGT-M or PGT-SR, depending on your situation. Your genetics team can help determine the best combination for your family.

Newer and emerging PGT technology

PGT-WGS: Whole genome sequencing

Some companies are expanding beyond standard testing to examine the entire genome of each embryo, not just the number of chromosomes or a few known variants. This approach is able to screen for thousands of rare, severe, often childhood-onset genetic conditions. I’ll note that this is not considered standard of care right now, though I definitely see the clinical utility.

Though the cost is high (but likely to decrease over time), this kind of comprehensive embryo testing holds a lot of promise. I’ve seen too many cases where an IVF pregnancy passed standard PGT-A testing, only for a serious single-gene condition to be discovered later, something current methods simply can’t catch. Genome sequencing-based PGT gives us the chance to learn much more about an embryo before transfer, allowing patients the opportunity to reduce risk of outcomes like these.

Interestingly, Juniper Genomics uses whole genome and transcriptome (RNA) sequencing for embryos. In addition to reporting on chromosome changes and single-gene disorders, the team created a new category of findings called “reduced viability variants.” These are genetic changes that are associated with failed implantation or pregnancy loss. This technology will be a game-changer, especially for those struggling with unexplained IVF failure.

PGT-P: Polygenic screening

Polygenic screening analyzes thousands to millions of genetic markers. The goal is to estimate risk for common, complex conditions like diabetes or mental health conditions, many of which are shaped by both genetics and environment. PGT-P is not meant to be diagnostic. Its predictive power is still evolving (particularly for individuals of non-European ancestry), and its clinical utility is not yet universally agreed upon. As with any emerging technology in the space, continued research, transparency, and honestly, comprehensive genetic counseling, will be key.

It’s crucial to understand the limitations of PGT

PGT results should be seen as screening, not a perfect diagnosis. Limitations include (but are not limited to):

• The biopsy samples only a few cells, which may not reflect the entire embryo.

• PGT (no matter the type) does not test for every condition.

• Maternal cell contamination can occur (where DNA from the mother skews results).

• And some genetic changes may occur after the time of the embryo biopsy, meaning they wouldn’t be detected at all.

It’s important to remember: PGT does not replace genetic testing during pregnancy.

PGT is powerful, but it’s only as useful as the way it’s understood and applied. So I’ll leave you with this: talk to a genetic counselor prior to selecting your PGT methodology… and then again to review your results.