What is PGS testing in IVF, and is it an outdated concept? Let’s clear things up

If you’ve been researching IVF, you’ve probably come across the term “PGS test" and perhaps also noticed “PGT-A” used in the same context. So, are they different, or has the terminology changed?

You’re not alone in feeling unsure. 

While both these terms are closely related, clinics have largely stopped using PGS (short for preimplantation genetic screening) in favor of more targeted terms that accurately describe what this test actually does. 

In this guide, we’ll explain what PGS is, how it fits into modern IVF care, and what you need to know about the available preimplantation genetic testing options today.

What is PGS in IVF?

Preimplantation genetic screening was used to detect chromosomal abnormalities in embryos during the IVF process and before implantation. With PGS embryo testing, doctors would identify embryos with the correct number of chromosomes (euploidy), associated with healthy embryo development and better chances of pregnancy success.

Source: Kelvin Agustinus

The medical community has mostly phased out the term PGS screening in favor of a broader and more accurate umbrella term: preimplantation genetic testing (PGT). The shift follows advancements in genetic research, as there are more refined ways to analyze embryo health today beyond basic chromosome counts.

Bonus read — Read our essential PGT guides:

• How long does preimplantation genetic testing take?

• IVF genetic testing

• IVF genetic testing pros and cons

• IVF timeline with genetic testing

What is PGT?

While the process of screening embryos hasn’t changed dramatically, the shift from PGS to PGT is more about clinical precision. The PGT framework includes a host of specialized tests designed to analyze genetic risks in different contexts, such as navigating a difficult fertility history or preventing inherited disorders. It demonstrates the advancing IVF space, which allows clinics and patients to have more agency during embryo selection on a case-by-case basis. 

The PGT framework includes three main types of genetic testing done on embryos: 

1. PGT-A: PGT for aneuploidy

2. PGT-M: PGT for monogenic disorders

3. PGT-SR: PGT for structural rearrangements

There are newer additions to PGT, such as PGT-P (for polygenic risk), which helps predict how a combination of genes from both parents affects potential risk of chronic and late-onset conditions (type 2 diabetes, cardiovascular issues, specific types of cancer).

1. What is PGT-A?

PGT-A examines embryos for chromosome number abnormalities, such as having too many or too few chromosomes, with a reasonable success rate. It is especially useful for women over 35 who face fertility decline or couples with recurrent pregnancy loss. Couples undergoing IVF with multiple embryos also use PGT-A to help choose the ones most likely to result in a healthy pregnancy.

PGT-A testing helps identify euploid embryos — those with the correct chromosome count — increasing the chances of successful implantation and a healthy baby. Here’s an overview:

Source: Edward Jenner

2. What is PGT-M?

PGT-A looks at chromosome numbers but doesn't detect specific genetic diseases. PGT-M, on the other hand, focuses on specific inherited conditions caused by changes in a single gene. These are often conditions that run in families, such as:

• Cystic fibrosis

• Tay-Sachs disease

• Sickle cell anemia

• Muscular dystrophy

• Huntington’s disease

• Hemophilia

• BRCA gene mutations, linked to increased cancer risk

PGT-M is typically used when one or both parents are known carriers of a genetic condition. Clinics typically design a personalized test based on the couple’s individual families and genetic backgrounds. 

Once embryos are created during IVF, specialists can analyze and flag those with the targeted gene mutation.

Read our PGT-A vs. PGT-M guide for more insights.

3. What is PGT-SR?

PGT-SR detects chromosomal structural changes in embryos, referring to alterations in how chromosomes are arranged, rather than how many there are. It’s a useful test to consider if you or your partner carries a known chromosomal rearrangement.

Types of structural changes PGT-SR locates include:

• Translocations: Segments of chromosomes are exchanged between two chromosomes.

• Inversions: A chromosome segment breaks off, flips, and reinserts in the opposite direction.

• Duplications: There is an extra copy of a gene segment. 

• Deletions: A portion of the chromosome is missing.

These rearrangements can be balanced or unbalanced. A balanced rearrangement means all the genetic material is present, but rearranged. People with balanced rearrangements often don’t show any detrimental symptoms.

Duplications and deletions are inherently considered unbalanced because there is either extra or missing genetic information. This can lead to developmental issues, miscarriage, or genetic disorders.

Note that even if the carriers are healthy themselves, they can pass on unbalanced versions of these rearrangements to children, which may lead to failed implantation, miscarriage, or serious developmental conditions.

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Why you may want to consider PGT-P testing

Beyond standard PGT tests, PGT-P testing can offer an additional layer of insights into embryos’ lifetime health risks — which can be especially useful if you have a genetic predisposition to conditions like diabetes and cancer. PGT-P looks at broader DNA insights to evaluate what risks each embryo carries for such chronic, adult-onset conditions.

For extra decision-making reassurance, you can also consider uploading your PGT-P data to Nucleus Embryo, a genetic optimization software that helps rank embryos based on health and well-being risk factors.

Pair your embryo testing with genetic optimization software

While PGT-SR and other testing methods help identify genetic risks and improve IVF outcomes, they offer a limited view. If you’re looking to go beyond viability and explore a broader picture of each embryo’s potential, go for a game-changing next step: using Nucleus Embryo software to compare embryos.

Nucleus Embryo is a next-generation genetic insight tool designed for people going through IVF. It expands on clinical PGT-P testing, offering you a fuller genetic profile of each embryo. You get to analyze and compare embryos across dozens of traits and conditions, including:

• Health conditions like cancer risk, heart disease, type 2 diabetes, ADHD, and numerous hereditary disorders

• Well-being markers related to sleep, learning, mental health, and more

Nucleus IVF+: Rooted in science, built for love

Preimplantation genetic testing helps identify the most viable embryos, but for many hopeful parents, it also leads to analysis paralysis.

With Nucleus IVF+, you’ll have access to:

1. Nucleus Family: Comprehensive carrier screening for over 2,000 inherited conditions

2. Nucleus Embryo: The first genetic optimization platform that helps you analyze, compare, and choose embryos based on health outlook, well-being indicators, and more

Nucleus Embryo is a genetic optimization solution designed for couples undergoing IVF who want a transparent overview of each embryo’s unique genetic potential. It’s not a replacement for PGT or medical advice, but a complementary tool to help you choose with your heart and head.

This platform allows you to sort, filter, and compare up to 20 embryos in a clear, intuitive, and supportive interface — so you see clear disease risks that could play a role in value-driven decision-making.

Get started today!

Nucleus also offers affordable DNA testing for carrier screening. You can order your at-home test kit if you need to research the disease risks you and your partner carry.

To get started with any Nucleus service, book a consultation with our experts.

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Featured image source: Nataliya Vaitkevich