Efficiency of extended blastocyst cultivation up to Day7

In clinics that allow extended culture up to Day7, on average 5% of embryos have a 48-hour delay in development. It has been showed that embryos from patients over 35 years of age take longer to form a blastocyst. The main aim - to evaluate the effect of extended embryo culture up to Day7 on embryo quality, ploidy and reproductive cycle outcomes. This was a retrospective cohort study in a private Delta Fertility Clinic of consecutive female infertility patients (n = 422) between Sept 2021-Sept 2022. Average age of the patients was 39,7 years who underwent frozen embryo transfer (FET) of a single euploid day 5, 6 or 7 blastocyst. Then we compared the outcomes in the 5Day, 6Day and 7Day groups.The results of culture and subsequent biopsy of trophoectoderm with PGT-A of 2095 blastocysts (1516 were tested with PGT-A) in 482 cycles were analyzed, of these, embryos Day7 suitable for biopsy were 9.8% (149). Blastocysts were classified as good (AA/AB/BA/BB) or poor (AC/BC/CA/CB). Cultivation performed in single drops, biopsy was performed using the flicking method. Statistical analysis was performed using the Pearson's Chi-Squared Test. In 3.4% of cases, patients had only Day7 blastocysts. Poor quality blastocysts were predominant in D7 blastocyst group (good quality: 91.0%, 65.2%, 46.3%; poor quality: 9.0%, 34.8%, 53.7%, P < 0.001 for D5, D6 and D7 blastocysts; respectively). The number of euploid embryos was significantly lower in the Day6 and Day7 group compared to Day5 (51.8% and 50.0% vs 64.4%, p