Your Guide to "Abnormal" PGT-A Results

Curated by DNAide Founder, Meaghan Doyle, MS, CGC

Last updated: March 6, 2023


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.

Guide Shortcuts
PGT-A 101
  • 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:

Not sure what some of these terms mean? View the definitions in the glossary.

  • 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
What it can look like on a report
What the result means
  • A mosaic result suggests that some of the cells tested were chromosomally normal (euploid) and some cells tested were chromosomally abnormal (aneuploid)

  • Mosaic embryos can self-correct and lead to healthy babies. This happens when abnormal cells die and the normal cells grow to compensate

  • Mosaic embryos may have lower implantation rates and higher miscarriage rates compared to euploid embryos

  • Babies born from mosaic embryos do not appear to have higher rates of birth defects or genetic syndromes compared to babies born from euploid embryos

Want to learn more?
No Result
What it can look like on a report
What the result means
  • The PGT laboratory could not produce a result for this embryo sample

  • This type of result does not mean an embryo is more or less likely to be abnormal. Chance for the embryo to be euploid is based on the age of the egg provider at egg retrieval

  • Re-biopsy of the embryo can be considered to try and obtain a result, depending on the quality of the embryo. Discuss the risks of re-biopsy with your healthcare provider

  • Embryo transfer may be considered without re-biopsy. Risk would be similar to an untested embryo.

Aneuploid Results

There are many different types of aneuploid PGT-A results, each with their own implications.

Types of aneuploid results
Segmental Aneuploid Results
What it can look like on a report
What the result means
  • A piece (segment) of a chromosome is missing or extra, rather than the entire copy of the chromosome

  • Abnormality is less likely to be present in the inner cell mass compared to other types of aneuploidy

  • Embryo may be mosaic even if it appeared that all cells tested had a segmental aneuploidy

  • Limited research available on this type of result

  • Not all PGT laboratories can detect/will report segmental aneuploidy

  • Re-biopsy of the embryo may provide insight into whether the embryo is fully aneuploid or mosaic. Discuss the risks of re-biopsy with your healthcare provider

  • If the egg or sperm provider are a carrier of a chromosome translocation the interpretation of this type of result is different. Talk to your healthcare provider(s) for more information.

Want to learn more?
Whole Chromosome Aneuploid Results
  • Result that does not indicate mosaicism or segmental aneuploidy

What it can look like on a report
What the result means
  • An entire copy of a chromosome is extra or missing

  • These types of results happen more commonly as age of the egg-provider increases

  • The inner cell mass usually contains the chromosome abnormality

  • If these embryos are transferred the most common outcome is failed implantation, with the second most common being early pregnancy loss

  • Chance of the embryo leading to a healthy live birth depends on the error rate of the test

Want to learn more?
Complex Aneuploid Results

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 three or more abnormalities, while others use it when there are two or more abnormalities. Some laboratories use a different term (chaotic) when there are 6 or more abnormalities while other labs still use the word complex.

What the result means
  • More than one chromosome abnormality was detected in the sample

  • The significance of the result depends on the types of abnormalities detected

    • if all abnormalities are mosaic, this is a mosaic result

    • if one abnormality is mosaic and the other is a whole chromosome aneuploidy, this is a whole chromosome aneuploid result

Want to learn more?
  • Register for our monthly webinar "All About Abnormal Embryos"

  • Book a detailed PGT result review with us to learn more about your aneuploid embryo(s)

Chaotic Results
  • Chaotic

What it looks like on a report
What the result means
  • 6 or more chromosome abnormalities were detected

  • Very limited research is available

  • These embryos have a higher chance of showing a euploid result on re-biopsy than is expected

  • Implications of this are still unknown

  • Re-biopsy of the embryo can be considered. Discuss the risks of re-biopsy with your healthcare provider

Chaotic results have only been studied by PGT lab Igenomix. It is not clear whether their research on chaotic results applies to chaotic results obtained from other laboratories.


Trophectoderm (TE): The area of the embryo that eventually develops into the placenta if a pregnancy forms. 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 forms. 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. 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

There are a lot of scientific terms used to discuss PGT results. Here are the definitions for many of them.

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