O-290 Clinical utility of putative mosaicism detected using concurrent copy-number and genotyping PGT method: outcomes from multisite, prospective, non-selection study including 9828 single embryo transfer cycles
Authors: Babariya D , Gill P , Tao X , Zhan Y , Figliuzzi M , Werner M , Jalas C , Capalbo A 
Published: June 2023

Abstract

Study question
What is the clinical utility and associated outcomes of mosaic whole chromosome or segmental aneuploidies detected using concurrent copy-number and genotyping analysis in PGT-A cycles?

Summary answer
Although high-level whole-chromosome mosaicism is linked to reduced sustained implantation, it has limited clinical significance in PGT-A cycles when co-evaluated with other clinical/ embryological factors

What is known already
NGS-based PGT-A can detect intermediate chromosomal copy number (CN), commonly interpreted as mosaic chromosomal aneuploidies in embryos. A prospective non-selection approach is the most effective way to assess the clinical utility of reporting putative mosaicism findings in PGT-A, wherein the presence of mosaicism is not disclosed and does not influence embryo selection. Conflicting results have been reported previously, possibly due to technological limitations in mosaicism assessment or retrospective analysis methods. This study reports the results of the largest multisite prospective non-selection clinical study examining the predictive value of whole-chromosome and segmental mosaicism, assessed through combined CN and genotyping data analysis.

Study design, size, duration
A multisite study involving seven IVF clinics was conducted from Feb 2020 to Oct 2022, including 6951 patients and 9828 single embryo transfers. The study involved a prospective non-selection approach, where embryos suspected of having whole chromosomal or segmental mosaicism were reported as negative for non-mosaic aneuploidies. Embryos were chosen for transfer based solely on standard morphological features. The primary outcome was sustained implantation rate (SIR) defined as pregnancy continuing beyond 8 weeks of gestation.

Participants/materials, setting, methods
In this study, the trophectoderm biopsies were analyzed using a custom, targeted NGS assay that examined approximately 5000 loci across the genome, providing genotyping information to support aneuploidy classification. Mosaicism was identified by any copy number deviation from the expected two copies (LogR plots) and confirmed by corresponding SNP B-allele frequency (BAF) patterns. Confounding factors, such as clinical and embryological variables, were controlled for in the multivariate analysis.

Main results and the role of chance
The average female age in this cohort was 34.9 years (SD = 4.1), with aneuploidy rate of 30% in embryos and SIR of 61.2%. Of the embryos transferred, 6.5% (636/9828) were whole chromosomal mosaic (WCM) only; 9.6% (947/9828) were segmental mosaic (SM) only and 1% (83/9829) were a combination of WCM and SM. The rate of putative mosaicism ranged from 15%-89%. The SIR of embryos in the control group (non-mosaic), SM and WCM were 62% (5190/8328; 95%CI), 58% (549/947;95%CI) and 50.3% (320/636; 95%CI P &lt; 0.01) respectively. A logistic model found that the level of WCM was associated to SIR, along with other embryological and clinical factors. In particular, WCM with a CN difference &gt;50% as well as poor embryo morphology were associated with lower SIR (OR = 0.5; 95% CI:0.32-0.76), but low-level (&lt;50%) mosaicism was not significant (NS). Notably, female age (OR = 0.98; 95% CI:0.97-0.99 per year), BMI (0.98; 95% CI:0.98-0.99) and previous ET failures (OR = 0.58; 95% CI:0.5-0.68) were strongly associated with SIR. A predictive model, taking into account all relevant variables, yielded a significant stratification of SIR, from 43% to 68%. Given the low incidence of WCM in our clinical setting, the multivariate SIR prediction (AUC) was 0.580 without WCM and 0.585 with mosaicism included.

Limitations, reasons for caution
This study did not have prenatal and post-natal data available at the time of the abstract's writing, hence conclusions about these outcomes wasn’t possible. Despite the large sample size, chromosome specific analysis was not feasible. Furthermore, this study’s data is platform-specific and cannot be translated to other PGT-A assays.

Wider implications of the findings
In this non-selection study, WCM of &gt; 50% variation was associated with lower SIR. However, high-level WCM has a minimal overall impact on SIR when co-evaluating with other clinical/ embryological parameters. Decisions on reporting criteria for these findings must weigh the risk of discarding potentially viable embryos with substantial reproductive potential.

Trial registration number
Not applicable