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

BackgroundNext 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 newborns chromosomal normalcy, have not yet been thoroughly determined. MethodsWe 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 newborns karyotype. ResultsLBR 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. ConclusionsThis 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)