Researchers in a 2020 study performed a clinical trial and transferred aneuploid embryos, finding that no whole chromosome aneuploids led to a live birth, while segmental aneuploids did.
PGS testing (PGT-A) is a technology that lets us take a closer look at the number of chromosomes the cells of an embryo has. Embryos with the right number of chromosomes, or 46 of them, are said to be euploid, while anything other than this number is said to be aneuploid.
Aneuploid embryos are thought to be the leading of miscarriage, particularly in older women who have a higher chance of producing aneuploid embryos. So the goal of PGS testing is to establish which embryos are euploid and which are aneuploid to transfer the euploid embryos that have a higher chance of success.
🔗 Original studies are referenced in this post or within the linked Remembryo posts.
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But PGS testing comes with controversy! Not everyone agrees that it is accurate. This is mainly because a typical biopsy for PGS testing only involves a few cells of a much larger embryo. And the worry is that this tiny biopsy, from which the euploid or aneuploid designation comes from, isn’t accurate. Aneuploid embryos are routinely discarded – but are they truly aneuploid? And would they work if they were transferred? One theory is that embryos can “self-correct” to go from abnormal to normal, although this is largely a phenomenon that’s thought to be restricted to mosaic embryos.
For more background on PGT-A, you can check my Complete guide to PGT-A (PGS testing).
A 2020 clinical trial that ran between 2014-2019 (Tiegs 2020) wanted to see what happens when aneuploid embryos were transferred.
Of course, for a doctor to knowingly transfer an aneuploid embryo that can lead to a miscarriage is a bit of an ethical nightmare, so they did something a bit sneaky. They performed the embryo biopsy, and transferred the embryo before getting the results of the test. So this way, if the embryo is aneuploid, no one knows at the time of transfer, and at least the doctor can sleep a little better at night.
So what were the results?
A total of 2110 blastocysts were biopsied and tested for PGT-A. 60.2% were euploid (1271/2110) and 24.6% were whole chromosome aneuploid (520/2110) – meaning they were not segmental aneuploids and the whole chromosome was impacted. Segmental aneuploids, mosaics, no-result, etc made up the rest.
In total, 414 transfers were performed. 312 of the embryos were euploid, of which 202 lead to sustained implantation or delivery (64.7%). The remaining 102 embryos were aneuploid and none of them (0%) progressed to sustained implantation or delivery.
40.2% of the women (41 women out of 102) who had transferred an aneuploid embryo had a positive pregnancy blood test and 24 of these women (23.5%) had a clinical pregnancy. All of these women experienced miscarriage after transferring an aneuploid embryo.
Besides the whole chromosome aneuploids that were transferred, 39 segmental aneuploids were also transferred of which 12 (30.8%) lead to sustained implantation/live birth. So segmental aneuploids may work after all! However, the authors mention that due to the low sample size, no statistical significance could be reported.
The authors conclude that aneuploids that are discarded do not have significant reproductive potential. And this may be the case – but there might be hope for segmental aneuploids!
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:
144 “abnormal” (aneuploid/mosaic) embryos and their outcomes
Segmental aneuploids: the main source for PGT-A false positives?
Chromosomal errors in IVF: What is aneuploidy and what causes it?
Segmental aneuploid embryos after PGT-A lead to healthy live births
Some embryos labeled as segmental aneuploid by PGT-A are actually euploid
Aneuploid embryo success rates after transfer
Aneuploid-only first PGT-A cycle has no impact on future PGT-A outcomes
Multiple embryo freeze/thaw for PGT-A doesn’t affect pregnancy or neonatal outcomes