JBRA Assisted Reproduction 2025;29(Suppl.2 SBRA 2025):7
Oral Presentation
29^th Annual Congress of the SBRA. São Paulo/SP - Brazil, 2025
doi: 10.5935/1518-0557.20263521

O-07. Impact of morphokinetic parameters during cleavage on blastocyst formation and clinical outcome in embryos monitored by time-lapse system

Amanda Turato Barbosa do Amaral¹, Alecsandra do Prado Gomes¹, Mariana Gomes Fujii¹, Tatiana Carvalho de Souza Bonetti², Pedro Augusto Araujo Monteleone^1,2

¹Centro de Reprodução Humana Monteleone - São Paulo - SP - Brasil
²Departamento de Ginecologia da Escola Paulista de Medicina - Universidade Federal de São Paulo (EPM-UNIFESP), São Paulo - SP - Brasil

Objective: Embryo selection is a crucial challenge in assisted reproductive technology. Effectively selecting the embryo with the highest developmental potential for transfer can significantly increase the success rates of in vitro fertilization (IVF) cycles. The time-lapse system (TLS) for embryo culture provides a continuous evaluation of morphological and dynamic embryonic parameters. TLS enables observation of embryo morphology across various developmental stages and records time parameters at each phase of development. The duration of the second cell cycle (CC2) and third cleavage synchrony (S3) have emerged as indicators of IVF success. However, their impact on blastocyst quality, developmental potential, and clinical pregnancy remains to be determined. This study aimed to evaluate the predictive value of CC2 and S3 for blastocyst development and quality, and to assess their influence on clinical pregnancy rates in single-embryo transfer cycles. In these cycles, selecting the embryo with the greatest potential for implantation is crucial.
Methods: This retrospective study was conducted in a private IVF clinic, including the analysis of 8,925 embryos developed from 15,090 injected oocytes, from 1,047 patients undergoing IVF cycles between 2021 and 2024 using a TLS for embryo culture. Embryo morphology and developmental dynamics were noninvasively observed by capturing images in the TLS and classification of blastocysts was performed. Moreover, the embryologists' team graded blastocyst expansion, inner cell mass (ICM), and trophectoderm (TE) epithelium quality according to the Gardner scoring system. The CC2 was calculated as the time interval between the first (two cells – t2) and second cleavages (four cells – t4). The S3 was calculated as the time interval between eight cells (t8) and five cells (t5), when the third cleavage starts. We have assessed the association of CC2 and S3 with embryo development, quality, and clinical pregnancy outcomes. Anonymized data for this study were extracted automatically from the electronic database system.
Results: Among 1,047 patients (mean women’s age: 38.0±4.0 years; men’s age: 40.5±6.3 years), 36.4% of cases presented advanced maternal age as the primary infertility factor. From 15,090 injected oocytes (MII rate: 90.5%; 2PN fertilization rate: 71.9%), 8,925 embryos developed, and 5,446 attained the blastocyst stage (61.0%). We construct a multifactor logistic regression equation for the correlation analysis between CC2 and blastocyst development or quality, as the S3 and blastocyst development or quality, and incorporate women's age as a confounder. The results showed an inverse association of CC2 and blastocyst development, as the CC2 increases, resulting in a significant reduction in the blastocyst development (OR: 0.875, 95% CI: 0.859–0.891, p<0.001). Similarly, top-quality (TQ) blastocyst significantly decreases when the CC2 increases (OR: 0.968, 95% CI: 0.9429–0.994, p=0.017). Moreover, there was an inverse association of S3 and blastocyst development, as the S3 increases resulted in a significant reduction in the blastocyst development (OR: 0.927, 95% CI: 0.921–0.932, p<0.001). TQ blastocyst significantly also decreases when the S3 increases (OR: 0.907, 95% CI: 0.899–0.914, p<0.001). Nonetheless, only shorter S3 correlated with successful clinical pregnancy after a single blastocyst transfer (n=938 embryo transfers) after adjustment for age, euploidy, male factor, and transfer type (OR 0.961, 95% CI 0.931–0.992; p=0.015). CC2 showed no significant association with pregnancy outcomes.
Conclusion: While both CC2 and S3 are predictors of blastocyst development and quality, S3 emerges as the sole independent predictor of clinical pregnancy. This underscores its critical utility in embryo selection algorithms to optimize IVF success rates. Importantly, our findings validate that non-invasive morphokinetic assessment—specifically S3 monitoring—provides a clinically reliable tool for identifying embryos with the highest implantation potential, reducing reliance on invasive procedures like PGT-A in routine cycles.