Segmental aneuploid embryos

Embryos tested with PGT-A may be found to have a segmental chromosome imbalance. Evidence is growing to show that some may be suitable for transfer. 

 

Fertility Genetics are supporting genetic counselling for a project with Juno Genetics to understand the potential of these embryos, as often clinics may not have a pathway in place for transfer. The work was presented at the Fertility 2026 by Emma Whitney - you can view the slides from the conference talk here where Emma emphasises that  

 

 

The text from the talk is copied below. If you are a clinic or a patient and have any questions, please get in touch. 

 

 

 

Slide 2: PGT-A was developed to allow us to use embryo biopsy to ‘see’ aneuploidy in embryos. But with the technology getting exponentially better and with the introduction of NGS we started to see things that we didn’t fully understand the implications around. By using SNP arrays with NGS we’ve pretty much cracked the use of Mosaic embryos, but a puzzle around segmental results still remains. 

 

Slide 3: Segmentals are a phenomenon where there is a duplication or deletion of only part of a chromosome. These embryos can pose a risk, we know that chromosomal deletions can result in serious genetic conditions such at Di Georges syndrome. 

 

Slide 4: We know from the JUNO Genetics EU Kim et al 2021 paper with re-biopsy of an embryo with a segmental ‘call’ you don’t always see it again in another biopsy result. Is this then most likely as the result of a mitotic error rather than coming from the gametes (eggs and sperm) themselves? 

 

The same paper showed that You can re-create the same whole chromosome aneuploidy call 99.9% of the time if you rebiopsy the embryo, even multiple times. Backing the science that whole chromosome aneuploidy is predominantly meiotic in origin and maternally age related. So these two genetic calls are distinctly different. 

 

Slide 5 and 6 With JUNO genetics PGT-A technology there is currently zero evidence of any live births resulting from embryos diagnosed with a whole chromosome aneuploidy. Tiegs et al 2021 

 

In the same non-selection study segmental aneuploidy embryos resulted in healthy live births when transferred 30.8% of the time Besser et al 2024 and Madjunkov et al 2025 recreated this with success rate of between 21-25% live birth rates. 

 

Slide 7: The evidence is growing but is there a way that we can be more sure? Can we find more information to help us select? 

 

Slide 8 The concept of using a re-biopsy strategy to see if it is a viable option to be able to reclassify some of these embryos as mosaic segmentals. Referencing Viotti et al data from 2021, where an upwards of a 43% live birth rate was even in mosaic segmental transfers. 

 

Slide 9-11 To ensure the process of re-biopsy was safe we looked at the Evewell’s own data over 2 years: We have biopsied 5142 embryos with good results. We have performed 227 thaw biopsy refreeze cases involving 534 embryos. 82 of those embryos have been used in SET with a 56% sustained implantation rate. 

 

Slide 12 Results of 38 segmental re-biopsies. It’s early days, but we have found that over 50% of these embryos, through re-biopsy can be reclassified as mosaic. 

 

Slide 13 take home message is we have to find a strategy that works. Discard of solely segmental PGT-A result embryos is no longer a viable or fair option to patients. 

 

It is not our duty to find the perfect embryo. It’s to realise the full potential of every embryo.