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Our findings suggest that vitrified oocytes result in similar pregnancy rates when compared to fresh oocytes with blastocyst transfer in an egg donation program. Moreover, vitrified oocytes may allow for a better cycle schedule, starting with a lower number of oocytes to be fertilized. Therefore, we hypothesize that egg banks with vitrified oocytes could be safely utilized in an egg donation program.

Objectives: To evaluate the association between morphology grading and morphokinetic parameters in blastocyst stage embryos cultured in a time-lapse system. Methods: This retrospective cohort study included patients offered fertility treatment with autologous oocytes in our clinic between October 2017 and May 2019 using a time-lapse system. The embryos were morphologically graded according to the criteria developed by Gardner and Schoolcraft and their morphokinetic parameters were recorded. Results: Our results indicated that the time of pronuclei fading (tPNf), time to cleavage into two (t2), four (t4), and eight (t8) cells, and time to start of blastulation (tB) were significantly different according to the morphological quality of the blastocysts formed. In the early development stage, tPNf, t2 and t4 differed between good (AA, AB, BA, BB) and poor (CC) quality potential blastocysts. The 8-cell stage time separated embryos graded as AA blastocysts in terms of morphology from embryos graded as BB. Earlier tB correlated with higher quality embryos (AA, AB, BA). Conclusion: Our results showed that the first kinetic parameters (tPNf, t2, and t4) distinguished top-graded from low-graded blastocysts. Between top-graded blastocysts, t8 separated BB blastocysts from AA blastocysts. And finally, tB also told apart BB blastocysts from AA, AB, and BA blastocysts. These time-related parameters may be applied even in centers without time-lapse systems.

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Study question How informative is the score grade of KIDScore version 3 for day 5 blastocyst for clinical pregnancy in biopsied and non-biopsied embryos? Summary answer Potential clinical pregnancy is predicable according to score grades (above 7.0), regardless the use of PGT-A, in blastocysts on day 5. What is known already Time-lapse technology has promoted, along with the use of artificial intelligence (A.I.), a new spectrum of tools to improve embryo selection. Several software and algorithms have been launched in ART field in the last years, with the perspective of providing a substantial boost in IVF outcomes. KIDScore is one of these new tools, developed based on morphology and morphokinetics of embryo development with known clinical outcome and validated with transfer of blastocyst on day 3 or 5. Yet, it is highly recommended an in-house validation of any A.I. tool before it started to be apply in clinical decisions. Study design, size, duration Retrospective cohort study in a single private IVF center. Positive or negative clinical pregnancy (fetal heartbeat and gestational sac presence/absence) record of patient’s autologous and donated cycles using fresh and frozen oocytes, with or without PGT-A embryos transfers using the Embryocope® Plus incubator, that underwent single embryo transfers (total sET, n = 415; euploid = 228, non-biopsied = 187) of blastocysts developed on day 5 were included. Biochemical pregnancy and miscarriage were excluded of this analysis. Participants/materials, setting, methods Negative and positive clinical pregnancy KIDScoreTMDay 5’s were stratified in three subgroups, according to V3 score intervals: subgroup 1: range between 1.0-3.9 (n = 29), subgroup 2: 4.0-6.9 (n = 154) and subgroup 3: 7.0-9.9 (n = 232). sET of euploid embryos (n = 228) were also analyzed in the described subgroups (subgroup 1: n = 17; subgroup 2: n = 93 and subgroup 3: n = 118, respectively). For the analysis, Mann-Whitney, Chi-square and Fisher tests were used for statistical analysis, values of p < 0.05 were considered significant. Main results and the role of chance Maternal age between overall positive and negative pregnancies were similar (38,48±3,86 versus 38,75±3,83,p = 0,3573). When comparing score subgroups, overall positive clinical pregnancy rates were significant different [subgroup 1: 20.7% (6/29); subgroup 2: 43.5% (67/154); subgroup 3: 63.8% (148/232),p < 0.0001]. When analyzing subgroup 1 versus subgroup 2 there was also a difference in positive clinical pregnancy (p = 0.023) and subgroup 3 also showed a higher rate in clinical pregnancy when compared to subgroup 1 and 2 together (scores from 1.0 to 6.9,p < 0.0001). Analyzing only euploid embryos, the results on positive clinical pregnancy were also significant different between subgroups [subgroup 1: 35.3% (6/17); subgroup 2: 45.2% (42/93); subgroup 3: 61.0% (72/118),p = 0,024, and subgroup 1 + 2 versus subgroup 3,p = 0,0115]. Maternal age between positive and negative clinical pregnancies in PGT-A cycles were similar (37,81±1,61 versus 38,38±3,25,p = 0,069). Analyzing only non-biopsied embryos, the results on positive clinical pregnancy were also significant different between subgroups [subgroup 1: 0.0% (0/12); subgroup 2: 41.0% (25/61); subgroup 3: 66.7% (76/114),p = 0,0343, and subgroup 1 + 2 versus subgroup 3,p < 0.0001]. Maternal age between positive and negative clinical pregnancies in non-biopsied cycles were also similar (39,40±4,75 versus 39,22±4,43,p = 0,7816). Positive clinical pregnancy in subgroup 3 were similar in biopsied and non-biopsied subgroups (61% versus 66.7%,p = 0.4133). Limitations, reasons for caution The retrospective nature and low data of subgroup 1 (1.0-3.9 score), since they naturally are the last option to be chosen for transfer. Wider implications of the findings Differences on positive clinical pregnancy between subgroups (mainly scores greater than 7.0) reinforce the use of A.I. as a complementary tool for embryo selection. Interestingly, positive clinical pregnancy in 7.0-9.9 subgroup were similar in euploid and non-biopsied embryos, strengthening another potential application of A.I. in transposing embryo aneuploidy barrier. Trial registration number Not Applicable