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Euploidy Predictability of Human Blastocyst Inner Cell Mass and Trophectoderm Grading

John B Whitney,Robert E Anderson, Nancy Nugent and Mitchel C Schiewe

 Background:

The selection of viable, potentially normal, embryos is vital to successful embryo transfers. Subjective morphology grading of blastocysts has been the most accepted and reliable standard to judge embryo quality. However, good to excellent embryo development alone does not necessarily insure euploidy. Our objective was to determine if independent quality grades for blastocyst inner cell mass (ICM) and trophectoderm (TE) can predict early embryo euploidy. Secondly, we aimed to develop a comparison chart for preference of blastocyst quality grades utilizing both ICM and TE grades to improve the decision make process.

 Methods and Findings:

Elective TE biopsy patients (n=139) underwent pre implantation genetic screening (PGS) for aneuploidy screening with subsequent embryo cryopreservation. The ICM/TE of day 5 and 6 blastocysts were independently graded (n>1200 blastocysts) from A to C: A=good to excellent, B=fair, and C=poor quality. All blastocysts achieved full blastocoel expansion prior to grading, laser-assisted blastocyst biopsying of the TE and then micro secure vitrification. Euploid embryos were subsequently selected for warming (>30 days post-PGS) and embryo transfer in 2014. Aneuploidy and pregnancy results were stratified by blastocyst grades. Combined quality grades determined an overall blastocyst grade and were further compared to evaluate preferences for euploidy. Chi-square analysis used to determine significance.

 Results:

Independent grade “A” blastocysts resulted in higher (p<0.05) euploidy predictability (56-62%) compared to “B” quality blastocyst (37-43%). Overall blastocyst quality revealed the TE grade was more predictive of euploidy. Upon warming, 100% embryo recovery and survival was achieved applying vitrification. Cumulative implantation and ongoing pregnancy rates were high at 82% and 78% respectively, with an overall low risk of spontaneous abortion (SAB; 5%). When comparing all quality grades of transferred blastocysts, no significance was observed for implantation, ongoing pregnancy or SAB percentages.