Does euploidy on day 5 or day 6 matter for clinical outcome in frozen single blastocyst transfers?

Abstract

Introduction Comprehensive chromosomal screening at the blastocyst stage by aCGH/NGS analysis has become increasingly common approach in order to obtain high implantation rates in ART. Although utilization of chromosomally screened blastocyst-stage embryos is known to provide superior clinical outcome, not all blastocysts display the same pace of embryo development and considerable number of embryos show delay in blastulation towards day 6 or day 7 instead of day 5. Attitudes of clinics towards delayed blastocysts largely differ in their PGT-A programs. Also, current literature on the comparative analysis of aneuploidy and clinical outcome of single euploid blastocyst transfer (SEBT) cycles involving a day 5 or a day 6 euploid blastocyst is scarce and contradictory. This study was conducted to analyze and compare the laboratory and clinical outcome of SEBT cases involving day 5 or day 6 euploid blastocysts screened by NGS. Material & Methods This retrospective study was conducted in Bahceci Fulya IVF Centre, between January 2016 and December 2017. It included a total of 1938 PGT-A cycles with indications of advanced maternal age, recurrent implantation failure or pregnancy loss. For all suitable embryos, a trophectoderm(TE) biopsy was performed on either on day 5 or day 6 and next generation sequencing (NGS) was used for comprehensive chromosomal screening (CCS) analysis. Of them, 658 frozen embryo transfers were performed as a single euploid blastocyst transfer (SEBT) cycle, with embryos biopsied on either day 5 (Group I) or day 6 (Group II). Major laboratory as well as clinical parameters were compared between groups. Results Main patient & cycle parameters were found to be similar in both SEBT groups (p>0.05). A total of 3501, 3111, 3010 (96.8%) and 1496 (49.7%) embryos in Group I and a total of 1540, 1280, 1242 (97.0%) and 511 (41.1%) embryos in Group II were biopsied, analyzed, diagnosed and detected as euploid respectively. Aneuploidy rate was found to be significantly high in embryos biopsied on day 6 (p=0.0024). Regarding laboratory parameters, although no difference was observed in terms of aneuploidy rates among embryos with different ICM scores, percent of embryos with trophectoderm score C was significantly high in Group II (p=0.018). Clinical outcome is shown in Table 1. Table 1: Clinical outcome between SEBT groups utilizing a day 5 or a day 6 blastocyst. Group I Group II p Num. of cycles (n) 498 160 Pregnancy rate (b-hCG+, %) 79.1 55.6 p Clinical pregnancy rate (Sac+, %) 72.7 52.5 p Live birth/Ongoing (%) 64.1 42.5 p Missed abortus (%) 11.3 17.9 NS Conclusions Our data and results have shown that, although they generate acceptable clinical pregnancies, euploid embryos that are obtained from embryo biopsies performed on day 6 result in significantly lower clinical outcome when compared to euploid embryos that are biopsied on day 5. This result further suggests that when there are more than one euploid embryo for SEBT, priority should be given to day 5-biopsied embryos in order to obtain better clinical outcome.