Choosing between Day 5 and Day 6 blastocyst: Comparison of aneuploidy rates and pregnancy rates

Abstract

Introduction Preimplantation genetic screening (PGS) can be performed on blastocysts formed on day 5 or 6. Several studies showed that embryos with delayed blastulation are associated with higher aneuploidy rate. Our study aimed to investigate if blastocysts developed on day 6 had higher rates of aneuploidy. We also compared the clinical outcomes (clinical pregnancy rate [cPR] and implantation rate [IR]) of transferring one frozen euploid blastocyst (day 5/6) post PGS. Can we expect equal outcomes for both blastocysts? Material & methods Retrospective study of intracytoplasmic sperm injection (ICSI) cases with PGS between January 2014 and December 2016. This study was divided into two arms: i) aneuploidy rates of day 5 and 6 blastocysts were analyzed on a per-embryo basis. ii) Outcomes of transferring single euploid day 5 or day 6 blastocyst in the subsequent frozen embryo transfer (FET) cycles were examined on per-patient basis. Embryos were assessed at 114-118 hours (day 5) and 138-142 hours (day 6). Only blastocysts of AA (3-6), AB (3-6), BA (3-6), BB (3-6) quality (modified Gardner blastocyst grading system) with protruding trophectoderm at the time of checking were selected for biopsy, based on the day they met the biopsy criteria. Biopsied embryos were vitrified and their ploidy status assessed using array comparative genomic hybridization. Only single embryo transfer was taken into consideration. Fisher's exact was used for statistical analysis. Results Among the 643 day 5 blastocysts analyzed, 340 (52.9%) were euploid and 303 (47.1%) were aneuploid. In contrast, day 6 blastocyst yielded significantly fewer euploid results with 67 of them (43.5%) being euploid and 87 (56.5%) aneuploid (p The outcomes of frozen embryo transfer were similar in women (32.2±5.8; n=87) who had either euploid day 5 or day 6 (33±5.8; n=15) blastocysts transfer. The cPR of transferring day 5 versus day 6 blastocyst was ([40/87] 46%vs 46.7% [7/15]); IPR = ([40/87] 46% vs 46.7% [7/15]) (p>0.05). Conclusions Our study showed that blastocysts with delay development, which formed on day 6 are associated with higher aneuploidy incidence. However, euploid blastocysts showed up on day 6 have similar chance of implantation as euploid blastocysts showed up on day 5. These data suggest that as long as the blastocysts are euploid, they are worth to transfer despite the day of its development. Topic for abstract submission: Clinical outcomes in PGT-A