O-155 Limited utility of mosaicism reporting in PGT-A: independent confirmation from a European multisite, double-blinded analysis including 4293 embryo transfers following the first US experience
Authors: Babariya D , Gill P , Ottolini C  S , Mulas F , Picchetta L , Caroselli S , Mounts E , Vergara Bravo V , Requena Miranda A , Pellicer A , García Velasco J  A , Zhan Y , Jalas C , Capalbo A 
Published: July 2024

Abstract

Study question
Are results showing limited clinical utility of mosaicism reporting in PGT from a blinded mosaic embryo transfer American study, confirmed in a European setting?

Summary answer
Even between different patient populations and clinical settings, putative mosaicism reporting has limited clinical utility for embryo selection when co-evaluated with other clinical/embryological factors.

What is known already
Intermediate chromosomal copy number (ICN) results in NGS-based PGT-A are commonly interpreted as embryo mosaicism. A recent prospective, non-selection study in America showed that reporting mosaicism would not significantly improve embryo selection. At odds with this, results suggesting that embryo selection based on putative mosaicism can improve clinical outcomes continue to be reported, possibly reflecting limitations in accurate mosaicism identification or retrospective analysis biases. This study replicates the design of previously reported American study, using the same PGT-A assay, examining the predictive value of whole-chromosome ICN (wICN) and segmental ICN (sICN) following concurrent copy-number and genotyping-PGT in a European setting.

Study design, size, duration
A multisite double-blinded study involving 14 European IVF clinics was conducted from April 2022 to July 2023, including 3365 patients and 4293 single embryo transfers. Embryos, reported as negative for uniform aneuploidies, including those with wICN or sICN, were chosen for transfer based solely on standard developmental and morphological evaluation. Primary outcome measure was live birth rate defined as any pregnancy reaching the 24th week of gestation (LBR).

Participants/materials, setting, methods
Trophectoderm biopsies were analysed using a validated targeted-NGS assay with approximately 5000 loci across the genome, providing both quantitative and genotyping information to support aneuploidy classification. Putative mosaicism was inferred from ICN deviations from the expected two copies for autosomes and partly supported by corresponding SNP B-allele frequency patterns. Related clinical and embryological variables were analysed in a multivariate analysis and a Random Forrest regression used to model the clinical utility of putative mosaicism.

Main results and the role of chance
Of the embryos transferred, 6.8% (293/4293) were wICN only; 6.2% (269/4293) were sICN only and 0.5% (23/4293) were a combination of wICN and sICN. The detected ICN ranged from 23%-84% with no overrepresentation of any individual chromosomes.
The LBR of embryos in the control group (without ICN), sICN and wICN were 46.8% (1736/3708; 95%CI:45.2-48.4%), 36.4% (98/269; 95%CI:30.9-42.3%) and 39.2% (115/293; 95%CI:33.8-44.9%) respectively. The miscarriage rate for control, sICN and wICN were 12.9% (257/1993; 95%CI:11.5-14-4%), 19.7% (24/122; 95%CI:13.6-27-6%) and 16.7% (23/138; 95%CI:11.4-23.8%), respectively. Logistic regression (P = 0.05) showed that the presence of sICN (OR: 0.7; 95%CI: 0.54-0.9) and wICN (OR: 0.62; 95%CI: 0.36-1.07) were modestly but significantly associated with LBR along with other embryological and clinical factors including embryo morphology (OR: 0.89; 95%CI: 0.84-0.96), day of biopsy (OR: 0.65;95%CI: 0.56-0.75), previous ET failures (OR: 0.79; 95%CI: 0.71-0.88) that were more strongly associated. No significant effect was observed of any specific intermediate CN cut-off on the association with LBR.
Random Forrest regression, considering all correlating variables, showed a LBR prediction (AUC) equal to 0.578 without putative mosaicism and AUC of 0.583 with putative mosaicism included, a negligible increase considering the low incidence of mosaicism in our clinical setting along with its modest predictive value.

Limitations, reasons for caution
Follow-up prenatal and post-natal data at this time was not available, hence conclusions about these outcomes wasn’t possible. Despite the overall large sample size, the analysis of specific effects at different ICN values lacked sufficient power. Furthermore, this study’s data is platform-specific and cannot be translated to other PGT-A assays.

Wider implications of the findings
Although putative mosaicism was associated with modestly impaired pregnancy rate, two independent studies now confirm that reporting mosaicism has limited impact when prospectively selecting embryos for transfer based on standard embryological parameters. Considering the established downsides, including potential embryo disposal, the practice of mosaicism reporting in PGT is questionable.

Trial registration number
Not applicable