Non-invasive Preimplantation Genetic Testing For Mosaic Embryos

Objective: To explore the value of non-invasive preimplantation genetic testing(ni-PGT)in the rediagnosis of embryos with chromosomal mosaic results in the previous PGT diagnosis,and to speculate the possible mechanism and dynamic process of different types of mosaic embryos according to the results of the secondary test.Methods: Data for patients enrolled for PGT treatment at a single center from 2014 to2019 were collected and the cycles with available mosaic embryos were evaluated.In the first part,in order to verify the diagnostic validity of ni-PGT,we thawed 8aneuploidy embryos,After 14-18 hours of reculture,we tested the concordance of the ni-PGT diagnosis results and the whole embryo test results.Then 41 mosaic embryos from 22 patients were included and underwent a 14-18 h re-culture.The genetic material of the BE,TE re-biopsy,and corresponding cell-free DNA in culture medium were amplified using multiple annealing and looping-based amplification cycles.The karyotype of ni PGT and TE re-biopsy were compared with the whole embryo,and the efficiency of ni PGT was assessed.Results: Data of 3738 blastocysts from 785 PGT-A and PGT-SR cycles of 677 patients were collected.Of the 3662(98%)successfully amplified embryos,849(23.2%)were euploid and 544(14.9%)were mosaic.Sixty patients without euploid embryos opted for a single mosaic embryos transfer,30(50%)of them obtained a clinical pregnancy.With BE chromosome copy number as the gold standard,SCM and TE rebiopsy showed better detection ability and diagnostic efficiency in 8aneuploidy thawed embryos.Of the 41 mosaic re-cultured and re-tested,35(85.4%)embryos showed actually euploid BE results.The raw concordance rates of SCM and TE re-biopsies compared with BE were 74.4% and 82% in terms of overall ploidy and96.2% and 97.9% per single chromosome when considering all degree mosaic results as true positives.However,when we set a mosaicism identification threshold of 50%,the concordance rates of SCM and TE re-biopsies compared with BE were 87.2% and85% at the overall ploidy level and 98.8% and 98.3% at the chromosomal level.At the full ploidy level,the sensitivity and false negative rates for ni PGT were 100% and 0,respectively.After adjustment of the threshold for mosaicism,the specificity of ni PGT increased from 69.7% to 84.8% in terms of overall ploidy and from 96.1% to 98.9%at the chromosomal level.Conclusion: This study was the first to explore the diagnostic value and clinical applicability of ni-PGT technology in embryos with chromosomal chimerism as a result of previous biopsy.This study presents a new opportunity for these patients who have only chimeric embryos available: regardless of the technical or biological basis of the chimera,culture solution testing for 14 to 18 hours after thawing and resuscitating may be the best option for maximizing the use of the embryo,as it has little invasive trauma to the embryo.