Day of embryo biopsy significantly affects the clinical outcome in obligatory but not elective frozen single euploid blastocyst transfers

Abstract

Recent studies have indicated that nearly a quarter of human embryos reach blastocyst stage on day 6 of embryo development and the use of a cryopreserved day 5 or a day 6 blastocyst produces similar clinical outcome in frozen embryo transfers (ET).It is also generally well-accepted that human embryo implantation is still considerably limited by the age-induced increase in aneuploidy. The application of PGT-A is proposed to diminish this negative effect by selecting euploid embryos for transfer. The aim of the current study is to analyze and compare whether a euploid day 5 and a day 6 blastocyst can result in similar clinical outcome in frozen single blastocyst transfers. Retrospective cohort study. Current study includes 584 frozen euploid single blastocyst transfer (ESBT) cycles performed between January 2016 and December 2017. Cycles were initially grouped and compared with respect to number of euploid embryos available for ET (Obligatory vs. elective ESBT) for their clinical outcome. An additional subgroup analysis was then performed according to maternal age (<40 years and ≥40 years) and the day of embryo biopsy (day 5 and day 6) within and between groups respectively. Basic patient/cycle characteristics, laboratory parameters including mean number of oocytes/m2 oocytes collected and fertilized as well as sperm parameters were comparable among matched groups (p˃0.05). A total of 353 obligatory and 231 elective ESBT cycles were performed. There were no statistically significant differences for clinical pregnancy rates (CPR; 68.2% vs. 69.7%), ongoing pregnancy/Live birth rates (OP/LBR; 58.1% vs. 64.5%) and implantation rates (IR; 68.8% vs. 69.6%) between groups (p>0.05). However, subgroup analysis showed significantly higher CPR, OP/LBR and IR in obligatory ESBT cases with <40 years of age utilizing day 5 biopsied embryos (81.4%, 71.4% and 82.1%) than cases utilizing day 6 embryos (50.6%, 42.3% and 50.6%; p<0.025). Although there is a tendency towards higher clinical outcome, differences observed in cases with <40 years diminished in obligatory ESBT cases with ≥40 years of age as well as elective ESBT groups respectively (p>0.05). Our results show that, once a euploid embryo is found, similar clinical outcome is obtained both in obligatory and elective ESBT cases utilizing biopsied and vitrified blastocysts irrespective of the day of embryo biopsy. On the other hand, Patients with <40 years of age undergoing obligatory euploid ESBT with day 5 biopsied embryos can have higher clinical outcome than the same group of patients utilizing day 6 biopsied embryos. Well-designed prospective studies with larger sample sizes are awaited to draw a firm conclusion on the real impact of biopsy day in such cases.