Researchers in a 2022 study reported on the outcomes of 144 “abnormal” embryos, consisting of aneuploids and mosaics, finding a single live birth with an aneuploid and more favorable results with mosaics.
How we define what makes an embryo aneuploid is changing as the technology of PGT-A advances.
Mosaic embryos have varying degrees of success and a number of studies (like this one) have been done to show that they are very capable of leading to live births, with some performing no different than euploid embryos. Despite this, there are still IVF centers that consider mosaic embryos as abnormal and refuse to transfer them.
Check my complete guide to mosaic embryos to learn more about mosaics, or my complete guide to PGT-A to get more background on PGT-A (aka PGS testing).
A new study by Barad et al. (2022, with the principle investigator as N. Gleicher) compared the outcomes of 144 “abnormal” embryo transfers, from 50 patients from 2014-2019. These abnormal embryos were a mix of aneuploid and mosaic embryos, which were nearly all tested by NGS, and pregnancy outcomes for these transfers were reported. The average age was 41 and most were considered poor prognosis.
🔗 Original studies are referenced in this post or within the linked Remembryo posts.
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76 of these embryos tested as non-complex aneuploids (aneuploids with <3 abnormal chromosomes) and 5 of them resulted in a pregnancy with 1 going on to a live birth. The aneuploid embryo that led to a live birth was originally tested as 46 XX + 14, -18 but a euploid female was delivered. This embryo was tested using microarray rather than NGS, and under current testing standards may have been classified differently (for example, as mosaic). Refer to Gleicher et al. 2023.
Another 30 were complex aneuploids (aneuploids with >3 abnormal chromosomes). In this group, 2 pregnancies resulted and both ended in miscarriage (100% pregnancy loss).
There were also 3 segmental aneuploids with one leading to a pregnancy and live birth. The segmental aneuploid was 46, XY, del (15) (q24.1-qter) but a euploid male was delivered.
If you’re unfamiliar with this complex/segmental terminology, you can review my post on understanding PGS testing results.
Besides aneuploids, there were 23 embryos that were mosaic: 15 were non-complex (9 pregnancies, 4 live births) and 8 were non-complex segmental (5 pregnancies, 2 live births). They didn’t give any information regarding whether or not these were high or low level mosaics.
Although this was a small study, it does illustrate that PGT-A can be effective in identifying aneuploid embryos that have a high chance of pregnancy loss. A previous study, which involved the transfer of 102 aneuploid embryos as determined by NGS, showed a similar result with 0 live births. This same study also found a good number of live births from segmental aneuploids, further suggesting that these embryos may be a good choice for transfer.
Note that my summary of this paper focuses on the outcomes of the NGS tested aneuploid and mosaic embryos separately. This paper uses the term “abnormal” to describe aneuploid and mosaic embryos, and reports the outcomes combined. As a result, it was confusing to isolate what was aneuploid or mosaic. The authors identify “non-complex abnormal” as embryos that contain: full chromosomal abnormalities, non-complex mosaic, non-complex segmental, and non-complex-segmental-mosaic. In this summary, I’m assuming the “full chromosomal” and “non-complex segmental” refer to non-complex aneuploid embryos that were not mosaic by NGS. Complex aneuploids were listed as “complex abnormal” and there was no indication that these were made up of any mosaic embryos.
Reference
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About Embryoman
Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.
Related posts:
IVF outcomes following aneuploid embryo transfer
Complete guide to PGT-A (PGS testing)
Complete guide to mosaic embryos
No difference in euploid and mosaic embryo transfers: a clinical trial
A look at how PGT-A results change with age, using data from over 86,000 biopsies
Segmental aneuploid embryos after PGT-A lead to healthy live births
Some embryos labeled as segmental aneuploid by PGT-A are actually euploid
Large study questions the value of reporting mosaic PGT-A results