A prospective double-blinded non-selection trial of reproductive outcomes and chromosomal normalcy of newborns derived from putative low/moderate-degree mosaic IVF embryos

Abstract

Background Next generation sequencing (NGS) has increased detection sensitivity of intermediate chromosome copy number variations (CNV) consistent with chromosomal mosaicism. Recently, this methodology has found application in preimplantation genetic testing (PGT) of trophectoderm (TE) biopsies collected from IVF-generated human embryos. As a consequence, the detection rate of intermediate CNV states in IVF embryos has drastically increased, posing questions about the accuracy in identifying genuine mosaicism in highly heterogeneous biological specimens. The association between analytical values consistent with mosaicism and the reproductive potential of the embryo, as well as newborn's chromosomal normalcy, have not yet been thoroughly determined. Methods We conducted a multicentre, double-blinded, non-selection trial including 1,190 patients undergoing in a total of 1,337 IVF with preimplantation genetic testing for aneuploidies (PGT-A) treatment cycles. NGS was performed on clinical TE biopsies collected from blastocyst-stage embryos. All embryos were reported as euploid if all autosomes had a chromosomal copy number value below the threshold of 50% abnormal cells per sample. After embryo transfer, three comparative classes were analysed: uniformly euploid profiles (<20% aneuploid cells), putative low-degree mosaicism (20%-30% aneuploid cells) or putative moderate-degree mosaicism (30%-50% aneuploid cells). Primary outcome measure was live birth rate (LBR) per transfer and newborn's karyotype. Results LBR after transfer of uniformly euploid embryos, low-degree, and moderate-degree mosaic embryos were 43.4% (95% C.I. 38.9 - 47.9), 42.9% (95% C.I. 37.1 - 48.9) and 42% (95% C.I. 33.4 - 50.9), respectively. No difference was detected for this primary outcome between euploid and mosaic low/moderate categories (OR= 0.96; 95% CI 0.743 to 1.263; P=0.816). The non-inferiority endpoint was met as the confidence interval for the difference fell below the planned 7.5% margin (95% C.I. -5.7 - 7.3). Likewise, no statistically significant difference was observed comparing moderate versus low degree mosaic embryos (P=0.92). Neonatal karyotypes were also similar and no instances of mosaicism or uniparental disomies (UPDs) were detected in babies born following putative low or moderate-degree mosaic embryo transfer. Should the embryos with low or moderate-degree mosaic TE biopsies had been classified as chromosomally abnormal and thus discarded for clinical use, LBR per cycle would have decreased by 36% without any clinical benefit. Conclusions This prospective non-selection trial provides substantial evidence that reporting and/or not transferring embryos with low/moderate-degree mosaicism for whole chromosomes have no clinical utility. Moreover, dismissing these embryos from clinical use has the counterproductive effect of reducing overall embryo availability, thus reducing the chance of successful outcome derived from an IVF treatment without any clinical benefit. (Funded by Igenomix; ClinicalTrials.gov number, NCT03673592)

Chromosomal mosaicism: Origins and clinical implications in preimplantation and prenatal diagnosis

“…The first prospective, nonselection randomized controlled trial has now reported that there are no differences in pregnancy and live birth outcomes from transfer of putative mosaic embryos up to 50% compared to euploid embryos. 35 There are multiple factors that can affect the detection of mosaicism in preimplantation embryos. A prime consideration is the extent to which a random sampling of 5-10 cells accurately reflects the genomic picture in the remainder of the embryo.…”

“…One major concern with mosaic embryo transfer studies is that the group receiving the putative mosaic embryos is enriched for patients where previous transfer with euploid embryos failed to implant. The first prospective, nonselection randomized controlled trial has now reported that there are no differences in pregnancy and live birth outcomes from transfer of putative mosaic embryos up to 50% compared to euploid embryos 35 …”

The “mosaic” embryo: misconceptions and misinterpretations in preimplantation genetic testing for aneuploidy

“…In addition, karyomapping analysis demonstrated that 36% of embryos with chromosome copy numbers in the intermediate mosaic range were actually euploid (9). In addition, embryos with ''low-level'' mosaicism have been shown to possess equivalent reproductive potential to embryos designated as euploid (10,11). As shown in Table 1, several studies have reported successful outcomes after the transfer of ''mosaic" embryos, and, coincidently, with an overall success rate of 38%.…”

“…An illustration of the impact of noise level on the accuracy of predicting euploidy (less noise) and error rate when predicting mosaicism (more noise) with simple copy number thresholds. ''putative'' mosaic embryos (10,33,42) or embryos with PGT-A profiles ''consistent with possible mosaicism'' (7). All clinical outcomes after the transfer of embryos designated as ''mosaic'' should be critically re-evaluated, with the idea that many of these embryos have been misclassified as mosaic and are actually uniformly euploid or uniformly aneuploid.…”

“…When aneuploidy originates from a meiotic error, all cells in the resulting embryo will possess the same aneuploidy (uniform). In addition, recent studies have demonstrated that embryos deemed ''low-level mosaic'' have equivalent reproductive potential to embryos deemed euploid (10,11).…”