Learning that you or your partner carry a structural rearrangement in your chromosomes can feel overwhelming, especially when you’re already experiencing the emotional and physical demands of IVF. You might be wondering what this means for your chances of pregnancy and whether it changes the road ahead.
PGT-SR is a form of preimplantation genetic testing designed specifically for this situation. It checks if embryos have inherited an unbalanced version of the rearrangement, which can prevent implantation or lead to pregnancy loss.
In this article, we’ll explain what PGT-SR testing is, how it works, who it’s recommended for, and what you can and can’t expect to learn from it. We’ll help you understand your options and make decisions that are right for your family.
What is PGT-SR?
PGT-SR (Preimplantation Genetic Testing for Structural Rearrangements) is a genetic test performed on embryos created through IVF. It detects chromosomal imbalances that stem from structural rearrangements in one of the parents’ DNA.
These structural changes can silently exist in a parent’s chromosomes without causing symptoms, yet they can significantly affect embryo development. When passed on to an embryo, they may lead to missing or extra pieces of genetic material, increasing the risk of:
Miscarriage
Implantation failure
Serious health conditions in a child
PGT-SR is one of three main types of preimplantation genetic testing available during IVF. Each test serves a distinct purpose depending on your genetic history and fertility journey:
PGT-SR | PGT-A | PGT-M | PGT-P |
Structural rearrangement-related imbalances, such as:
| Aneuploidies — missing or extra chromosomes, causing conditions such as:
| Specific inherited single-gene disorders, such as:
| Polygenic conditions (complex or late-onset conditions influenced by multiple genes), such as:
|
PGT-SR, PGT-P, and other genetic testing options are an excellent way to reduce uncertainty, protect your emotional well-being, and feel more in control during a stressful process, as one parent describes:
Bonus read — Read about additional genetic testing options in more detail:
How does the PGT-SR test work?
The PGT-SR testing process fits seamlessly into a standard IVF cycle. The main steps are:
Embryo development and biopsy
Lab analysis and results
Embryo selection and transfer
Each step is explained in more detail in the sections below.
1. Embryo development and biopsy for PGT-SR testing
All forms of preimplantation genetic testing, including PGT-SR, are performed on embryos, not eggs or sperm so that testing can only be done as part of an IVF cycle.
During IVF, eggs are retrieved from the ovaries and fertilized with sperm in the lab. The resulting embryos are then closely monitored as they grow. Around day 5 or 6, the healthiest embryos usually reach the blastocyst stage.
At the blastocyst stage, the embryo has two main parts:
The inner cell mass, which will eventually become the fetus
The trophectoderm, which develops into the placenta
To test the embryo without potentially harming its future development, a few cells are carefully removed from the trophectoderm. This area is chosen because it allows the inner cell mass — the part that forms the baby — to remain untouched and protected.
This small biopsy doesn't damage the embryo or affect its ability to implant and grow, making the process highly safe.
Source: Vika Glitter
After the biopsy, all embryos are frozen while the lab completes testing. This is a standard and completely safe practice, as it gives the lab time to analyze the cells carefully and report results without rushing the embryo transfer process. Freezing also allows your body to rest and recover from the egg retrieval before preparing for pregnancy.
2. Lab analysis and results
Biopsied embryo cells are sent to a lab, where scientists examine structural rearrangements and, when relevant, whole chromosome imbalances.
The most common structural rearrangements include:
Translocations: A piece of one chromosome breaks off and attaches to a different chromosome. Most commonly, they are:
Reciprocal translocations, when segments are swapped between two chromosomes.
Robertsonian translocations, when two chromosomes fuse into one.
Inversions: A segment breaks off, flips, and reattaches in the reverse direction.
Duplications: A chromosome piece is copied one or more times, leading to extra genetic material.
Deletions: A piece of a chromosome is lost.
Your results are ready in one to five weeks after receiving the samples, and they show if each embryo is:
Normal: Has the standard chromosomal structure.
Balanced: All the genetic material is there, but some pieces may be in different places. The rearrangement may be the same as in a parent.
Unbalanced: Parts of chromosomes are missing or repeated.
Results may sometimes be inconclusive, meaning the lab couldn’t determine the embryo’s status with certainty, prompting your clinic to recommend further testing or genetic counseling.
Most people with a balanced rearrangement are healthy and may never know they carry one until they experience challenges trying to conceive. In rare cases, a balanced rearrangement can disrupt a gene’s function, potentially leading to health issues.
However, people with balanced rearrangements are at a higher risk of passing on an unbalanced version to their children, which can interfere with healthy development. The severity depends on the affected genes and the amount of genetic material involved.
3. Embryo selection and transfer
Once the lab sends the report to your fertility clinic, your doctor will review the results with you and help identify which embryos are suitable for transfer. Embryos that are either normal or balanced are considered for transfer, as they have the best chance of resulting in a healthy pregnancy.
Source: Edward Jenner
Once you’re ready, a frozen embryo transfer can be scheduled. This involves thawing one of the healthy embryos and placing it into your uterus during a carefully timed cycle. Frozen transfers are as successful as fresh transfers — and often more so because your body can be fully prepared.
Any remaining embryos that are found to be normal or balanced can also be frozen and stored for future use.
For many families, choosing which embryo to transfer isn't just about whether it's balanced or unbalanced, but also about how confident they feel in the decision. Here's how one parent described their experience:
💡 Tip
After PGT-SR, you may have more than one embryo labeled normal or balanced. That’s great news, but it also leaves you facing another difficult decision — which embryo to transfer first?
While PGT-SR screens for structural and chromosomal issues, it doesn’t compare embryos beyond that. PGT-P can give you more comprehensive insights on the long-term health outcomes of embryos.
Nucleus Embryo can offer deeper insights by analyzing additional factors that impact your future child’s development, health, and physical characteristics. The genetic optimization tool outlines your embryos’ risks for common conditions and traits, such as type 2 diabetes or heart disease, cancers, eye color, and IQ.
All of this is delivered through an interactive, easy-to-understand dashboard so that the results are useful to parents who want to make a transparent and responsible decision. No complex jargon — just clear, science-backed information to help you compare and filter embryos based on comprehensive genetic data.
If you’re trying to decide between two (or more) embryos, book a consultation with our experts to see how Nucleus can help you get the clarity you need.
When is PGT-SR testing recommended?
Because many carriers of chromosomal rearrangements show no symptoms, they often don’t realize there’s a risk until they face repeated losses or a failed IVF cycle. If there’s reason to suspect that you or your partner carry a balanced structural rearrangement, your doctor will recommend PGT-SR testing. Here are the most common scenarios:
Recurrent miscarriage: If you’ve experienced two or more pregnancy losses, one possible culprit could be an unbalanced chromosome rearrangement in an embryo.
Known carrier of a structural rearrangement: Many carriers are first identified during a fertility workup or after genetic counseling.
Previous child or pregnancy affected by an unbalanced rearrangement: If a past pregnancy delivered a baby with a chromosomal condition, or genetic testing revealed an unbalanced rearrangement, PGT-SR can screen future embryos to lower the chance of recurrence.
Before proceeding with PGT-SR, most clinics require genetic counseling to review your personal and family history, explain what different rearrangements mean, and help you weigh the emotional and financial considerations.
Source: ShotPot
How accurate is PGT-SR?
PGT-SR is highly accurate in identifying chromosomal rearrangements, with detection rates typically above 98% when performed by a certified lab using high-quality biopsied samples.
A good sample means that the biopsy captured enough healthy cells from the right part of the embryo, and the DNA is intact and not degraded.
However, like all genetic tests, PGT-SR is not perfect. There are a few important limitations to understand:
Mosaicism: In some embryos, not all cells are the same genetically. Some may carry a rearrangement while others don’t, making results harder to interpret or less reliable.
Undetectable rearrangements: Some structural changes are so small or uncommon that they may be difficult to detect with current testing methods, especially if they aren’t associated with a known, identified issue in one of the parents.
PGT-SR only detects specific conditions: PGT-SR is typically recommended after a structural rearrangement is identified through genetic counseling and karyotyping of the parents. It’s not a broad screening tool for all chromosome or gene-level problems.
Bonus read — Learn more about genetic testing in our other guides:
What PGT-SR can and can't do
PGT-SR can significantly improve the chances of a healthy pregnancy, but it doesn't guarantee a perfect outcome. It's important to understand what PGT-SR can and can't do, so you can decide whether additional tests or insights might help guide your IVF journey:
What PGT-SR can do | What PGT-SR can’t do |
|
|
PGT-SR can provide helpful guidance, but it doesn't always offer a clear answer, especially when multiple embryos appear viable. And while it's a valuable tool, it can't predict everything about an embryo's health or long-term potential.
If you’re looking for insights that go beyond basic chromosomal screening, additional tools may offer more clarity.
Nucleus IVF+: Genetic insights that help you decide
The Nucleus Embryo platform goes beyond structural rearrangements and uses robust PGT-P analyses to give you a broader, more holistic view of each embryo’s potential.
While traditional genetic tests focus on large-scale chromosomal issues, Nucleus extracts the more granular PGT-P data to analyze your embryos’ risk for developing complex, multi-factorial conditions that are chronic, hard-to-predict, and often show up later in the lifetime.
Nucleus will then analyze your PGT data further to uncover additional layers of information, including common and rare diseases, and physical and personality traits. This goes beyond basic viability and gives you and your partner the opportunity to choose embryos based on what matters most to you.
Common diseases | Physical traits |
|
|
You’ll see each embryo laid out side by side in a clear, interactive dashboard with jargon-free explanations.
For those who want to go even deeper, optional Nucleus Family carrier screening analysis can provide additional layers of information. Nucleus Family screens for hundreds more conditions than any other carrier screening test on the market, ensuring you don’t unknowingly pass risks down to your children.
Book an onboarding call today to see how you can incorporate Nucleus Embryo in your IVF journey.
You may also like…
Featured image source: Pavel Danilyuk
