L26/P-549 Association between preimplantation morphokinetics and implantation in euploid blastocysts: a multicenter time-lapse study

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Abstract Study question Are preimplantation morphokinetic timepoints associated with implantation outcomes in euploid embryos after transfer? Summary answer Euploid blastocysts that implanted reached developmental milestones t5, t8, and tB earlier than non-implanting embryos. What is known already Several studies have investigated the association between morphokinetic parameters and implantation outcomes using time-lapse imaging; however, their clinical utility for predicting implantation remains uncertain. Importantly, many of these studies did not control for embryo ploidy, one of the strongest determinants of implantation potential. Even though transfer of euploid embryos significantly improves implantation rates, a substantial proportion of euploid blastocysts still fail to implant, underscoring the contribution of factors beyond chromosomal status. It therefore remains unknown whether differences in morphokinetic timing among euploid embryos capture biologically meaningful differences related to implantation competence, or simply reflect global developmental variability. Study design, size, duration Retrospective, international, multicenter study including 672 PGT-A cycles resulting in at least one euploid transfer, performed between June 2019 and October 2024, across three private fertility clinics. A total of 741 euploid blastocysts transfers with available morphokinetic data and implantation outcomes were analyzed. Implantation was defined as ultrasound detection of an intrauterine gestational sac at 6-7 weeks. Biochemical pregnancy was defined as a positive serum ß-hCG test that did not progress to an ultrasound-confirmed pregnancy. Participants/materials, setting, methods Preimplantational development was monitored using time-lapse imaging to track key morphokinetic timepoints (tPNf, t2, t3, t4, t5, t8, tSB and tB). Kaplan-Meier survival curves were built for each morphokinetic parameter and implantation outcome group; and were analysed using Cox proportional hazards models adjusted for maternal age and center. Developmental trajectories were identified using unsupervised k-means clustering. Associations between trajectory clusters and implantation outcomes were tested using multivariate mixed-effects logistic regression models. P-values<0.05 were considered significant. Main results and the role of chance Mean maternal age (±SD) was 37.8 (±3.9) years. Among 741 euploid blastocyst transfers, 57.49% (n = 426) resulted in implantation, 37.25% (n = 276) failed to implant and 5.26% (n = 39) resulted in biochemical pregnancy. Early morphokinetic parameters, including tPNf, t2, t3, t4 did not differ significantly between embryos that implanted and those that did not. In contrast, implanting embryos reached later developmental timepoints faster than non-implanting embryos, particularly the 5-cell stage (t5: HR = 1.21, 95% CI (1.04-1.41), p-value=0.01), 8-cell stage (t8: HR = 1.19, 95% CI (1.02-1.38), p-value=0.02), and blastocyst stage (tB: HR = 1.17, 95%CI (1.01-1.36), p-value=0.03) in Cox regression models adjusted for maternal age and center. On average, implanting embryos reached t8 and tB approximately 2 and 1.5h earlier, respectively. Unsupervised clustering identified fast, intermediate, and slow developmental trajectories, with progressively lower implantation rates from fast to slow. In mixed-effects logistic regression, embryos in the slowest trajectory had significantly reduced implantation odds compared with the fastest (OR = 0.46, 95%CI (0.28–0.77), p = 0.003), whereas differences between fast and intermediate trajectories were not significant. These findings indicate a gradual association between global developmental tempo and implantation, rather than discrete morphokinetic classes. Euploid embryos resulting in biochemical pregnancies showed slower development, but the differences were not statistically significant. Limitations, reasons for caution This retrospective study was restricted to cycles with euploid blastocyst transfer, which may limit generalizability. Although the observed morphokinetic differences were statistically significant, effects were small and continuous. Residual confounding related to culture environment, image annotation, or uterine factors cannot be fully excluded. Wider implications of the findings Among euploid embryos, faster progression through late preimplantation stages showed modest association with implantation, suggesting that morphokinetics reflect overall developmental competence rather than discrete determinants of implantation success. Morphokinetic parameters appear to have limited standalone utility but may provide complementary value when integrated with ploidy status and clinical context. Trial registration number No

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