LAUSR

Is there any difference in blastocyst morphology, embryo aneuploidy rate and ART clinical outcomes when using fresh or vitrified donor oocytes? Frequency of good quality blastocyst obtained from fresh oocytes is significantly higher compared to vitrified.No difference in embryo aneuploidy rates nor clinical outcomes were found. Oocytes vitrification is an efficient method that allows non only fertility preservation but also the creation of donor oocytes banks, optimizing clinical resources for patients undergoing Assisted Reproductive Technology. Although the benefits of donor oocytes vitrification are well known, some studies have shown that this cryopreservation process can induce spindle abnormalities and chromosomal changes, leading to aneuploidy. Comparative studies between fresh and vitrified oocytes to evaluate embryo developmental competence, aneuploidy and clinical pregnancy rate (CPR) are needed. This retrospective study includes ICSI cycles with fresh donor oocytes(N = 2795) and vitrified donor oocytes (N = 1225) between January 2019 and September 2020. Pre-implantation Genetic Testing for Aneuploidy (PGT-A) was performed on Day 5 and Day 6 blastocysts. Fertilization rate, blastocyst morphology, aneuploidy status and CPR were analysed and compared between the groups. Recipients were equally distributed in terms of maternal age (40.86 years) and previous history, sperm samples were also similar in profile and origin (fresh-frozen). A total of 266 subfertile couples participated in the study, ICSI was carried out in all cycles. Vitrification and warming protocols were performed with a commercial kit. All embryos were cultured to blastocyst stage in a Time-Lapse incubator and assessed by Gardner’s blastocyst grading scale. PGT-A testing was performed on trophectoderm biopsies by Next Generation Sequencing (NGS). Single/double embryo transfers were performed in all cases. Odd-ratios were calculated,and Chi-square was performed for the statistical analysis. A total of 266 patients underwent 289 donor oocyte cycles yielding an overall of 4557 oocytes. ICSI was performed on 2795 fresh and 1225 vitrified mature oocytes. Similar fertilization rates were achieved with fresh and vitrified oocytes (75.9% (2122/2795) and 75.2% (921/1225), respectively (P = 0.6)) yielding a significant difference in blastocyst rate of 71.7% (1522/2122) and 62.5% (576/921) (OR 1,519; 95% CI 1,290–1,789; p < 0.001). In addition, when blastocysts morphology was analysed, a significant difference was shown in the frequency of good quality embryos that decreases from 56.6% (861/1522) with fresh oocytes to 51% (294/576) with vitrified oocytes (OR 1,249; 95% CI 1,031–1,514; P < 0.02). PGT-A testing of blastocysts revealed not significant differences in euploidy rates (73.6% in fresh oocytes vs 76.8% vitrified oocytes, P = 0.2). With regards to clinical outcomes, similar results were found between the groups. A total of 322 embryo transfers were performed (237 from fresh and 85 vitrified) achieving a CPR of 48.9% (116/237) with fresh oocytes and 54% (46/85) with vitrified (P = 0.7) and a pregnancy loss of 6.7%(16/237) in fresh oocytes and 11.7%(10/85) vitrified oocytes (P = 0.1). The study was conducted on a small number of cases. Further studies are needed to confirm our findings. Moreover, although the same stimulation protocol was used, donors from different background were included. Wider implications of the findings: This study supports the use of vitrified oocytes in the laboratory routine without compromising clinical outcomes. Although oocyte vitrification may have an influence on embryo morphology, blastocyst rate, no impact of this cryopreservation process is seen on embryo aneuploidy, developmental competence and CPR. Not applicable