Your Guide to “Abnormal” PGT-A Results
Curated by Meaghan Doyle, MS, CGC
Last updated November 10, 2023
Introduction
At DNAide it is our mission to make information about fertility genetics more accessible. This guide provides an overview about the different types of "abnormal" (non-euploid) results that you might get after preimplantation genetic testing for aneuploidy (PGT-A).
This information is for general informational and educational purposes only. It is not a substitute for medical/professional advice or genetic counselling.
Want more information about your results after reviewing this guide? Schedule a genetic counselling appointment with us here.
PGT-A 101
Not sure what some of these terms mean? Check our GLOSSARY
To perform PGT-A a sample of 5-10 cells are removed from the trophectoderm of the embryo
The trophectoderm will eventually develop into the placenta
The inner cell mass is the area of the embryo which would eventually develop into the baby. These cells cannot be tested
PGT-A is not 100% accurate. The "accuracy" of PGT-A depends on BOTH of the following:
The likelihood that the genetics of the trophectoderm matches the inner cell mass
The ability of the test itself to accurately reflect the genetics of the cells being tested
Mosaic Results
Mosaic is an intermediate PGT-A result. It suggests that some cells tested were euploid and some cells tested were aneuploid but there are a few reasons why a mosaic result can happen.
Embryos with mosaic results generally have lower implantation rates and higher miscarriage rates compared to embryos with euploid results. There are many different categories of mosaic results and some can have outcomes similar to embryos with euploid results.
Most babies born from embryos with mosaic results have normal chromosomes. It is important to meet with a genetic counsellor to learn more about your specific result because some may have higher risks than others.
Sample Reports
It’s in the name; this means that the PGT-A laboratory couldn’t report a result for this embryo. This result doesn’t mean the embryo is more or less likely to be normal. It has the same chance of being euploid or aneuploid as it did before it was tested. The chance of the embryo being euploid is based on how old the egg provider was when they had their egg retrieval.
Depending on the quality (grading/morphology) of the embryo, rebiopsy can be considered. This comes with risk so make sure you discuss this with your health care providers in detail.
Transfer of an embryo with no result can often be considered as well. Outcomes are expected to be similar to embryos that are not tested. Talk to your healthcare team to learn more about this option
No Result
Sample Report
Aneuploid Results
There are many different sub-types of aneuploid PGT-A results, each with their own implications.
Whole Chromosome Aneuploid
This is an aneuploid result that shows no sign of mosaicism (discussed above) or segmental aneuploidy (discussed below). It means that the results showed an entire copy of a chromosome missing (monosomy) or extra (trisomy).
These results happen more frequently as the age of the egg provider increases.
This is the most accurate type of aneuploid result. The inner cell mass is likely to contain the same aneuploidy. If embryos with this type of result are transferred the most likely outcomes are lack of implantation or early pregnancy loss.
The chance of an embryo with this type of result leading to a healthy live birth depends on the error rate of the specific PGT-A laboratory.
Sample Reports
Segmental aneuploid means that a piece (segment) of a chromosome is missing or extra, rather than the entire copy of the chromosome. It may also be referred to as a partial monosomy or partial trisomy. You may see the letters p and q included on a report for a segmental aneuploid. These letters help describe which segment of the chromosome is impacted by the aneuploidy.
Segmental aneuploid results are different from segmental mosaic results.
Research suggests that when PGT-A detects a segmental aneuploidy, there is a lower chance that the aneuploidy will be present throughout the whole embryo compared to other sub-types of aneuploid results. This means there is a higher chance the embryo may be mosaic, even when mosaicism wasn’t detected in the sample tested.
There isn’t research looking at the outcomes when people transfer embryos with this type of result. This means we don’t have statistics on implantation rates, miscarriage rates, live birth rates, and whether there are higher rates of babies born with genetic syndromes from these embryos.
Not all laboratories can detect or choose to report segmental aneuploidies. Check the fine print, or speak with a genetic counselor from the laboratory to learn more.
NOTE: If the egg or sperm provider are carriers of a chromosome rearrangement, like a translocation, the interpretation of this type of result is different. Talk to your healthcare provider(s) to learn more.
Segmental Aneuploid
Sample Reports
Complex Aneuploid
Different PGT laboratories have different definitions of 'complex' aneuploid results. Typically this word is used when an embryo is found to have more than one chromosome abnormality. Some laboratories use the term complex when the embryo has two or more abnormalities, while others use it when there are three or more abnormalities. Some laboratories use a different term, “chaotic” (discussed below) when there are 6 or more abnormalities while other labs still use the word complex.
The meaning of this result type depends on the individual aneuploidies that are detected (e.g. mosaic, segmental, etc.).
This is another sub-type of aneuploid result that can have different meanings at different PGT-A laboratories. This guide will discuss the meaning of a chaotic result when tested by PGT-A laboratory Igenomix only.
Igenomix will explicitly write the word “chaotic” when an embryo belongs to this sub-category of aneuploid results.
An embryo with a chaotic result from Igenomix has 6 or more abnormalities detected. Very limited research has been performed on embryos with this type of result. Research showed that embryos with this result type had a higher chance of showing a euploid result when rebiopsied than expected. We don’t know if this means that the embryo is mosaic, or if one of the biopsy samples is an incorrect result.
Rebiopsy of embryos with this type of result can be considered depending on the quality (grading/morphology) of the embryo. Discuss the risks with your healthcare provider(s) to ensure this option applies to your embryo.
Chaotic
Glossary
We use a lot of scientific terms to discuss PGT-A. Here are the definitions for many of them.
Trophectoderm (TE): The area of the embryo that eventually develops into the placenta if a pregnancy occurs. Cells of the trophectoderm are biopsied (removed) and tested when PGT is performed
Inner Cell Mass (ICM): The area of the embryo that eventually develops into the baby if a pregnancy occurs. Cells of the inner cell mass are not tested when PGT is performed as it is not safe to remove them from the embryo.
PGT-A: Preimplantation Genetic Testing for Aneuploidy
Viability: The ability of an embryo to lead to a pregnancy.
Euploid: A normal result on PGT-A. No chromosome abnormalities are detected within the scope of the test. The “normal” number of chromosomes.
Chromosomes: The packages that carry all of our genes. The "instruction books" for a developing embryo.
Translocation: A chromosome rearrangement where chromosomes break and reattach to different chromosomes.
Monosomy: There is one copy of a chromosome when there should be two
Trisomy: There are three copies of a chromosome when there should be two
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