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Aim: To compare clinical outcomes using short and long co-incubation protocols in sibling oocytes based on embryo morphokinetic outcomes measured by time-lapse incubator with stratification based on a woman's age and sperm quality., Design: Our study included 72 cycles with >6 oocytes retrieved. Sibling oocytes were distributed for two parallel protocols: short (3 h; n = 421) or long (16-20 h; n = 434) insemination, using the same amount of spermatozoa from the same prepared sample. Oocytes were then washed and incubated for 5 days. Time-lapse annotations of embryos were performed by experienced embryologists and artificial intelligence-based Known Implantation Data scores for day 3 and day 5 were calculated with EmbryoScope software., Results: Short-insemination group exhibited a higher blastulation rate, better morphokinetic indicators, and higher Known Implantation Data scores on day 3 and day 5 of the utilized embryos. However, the fertilization rate and clinical pregnancy rate per embryo transfer did not differ between experimental groups. A higher rate of abnormal fertilization (>2 pronuclei) after long insemination was recorded in women under 35 years old or with a total motile sperm count above 5 million and above 40% motility after preparation. A higher rate of usable embryos was observed after short insemination with a total motile sperm count above 30 million before preparation or 5 million and over 40% motility after preparation., Conclusions: Our results suggest that a short insemination protocol results in better embryo quality and should be considered as a favorable protocol, especially in young female patients or male patients with high sperm quality., (© 2024 American Society of Andrology and European Academy of Andrology.)

The increased use of vitrified blastocysts has encouraged the development of various criteria for selecting the embryo most likely to implant. Post-thaw assessment methods and timetables vary among investigators. We investigated the predictive value of well-defined measurements of human blastocyst re-expansion, following a fixed incubation period. Post-thaw measurements were taken exactly at 0 and 120 ± 15 min. Minimum and maximum cross-sectional axes were measured. Three groups were defined: Group 1: embryos that continued to shrink by 10 µm or more; group 2: embryos that ranged from -9 to +9 µm; and group 3: re-expansion of 10 µm or more. Patient and morphokinetic data were collected and integrated into the analysis. A total of 115 cases were included. The clinical pregnancy rate for group 1 was 18.9%; group 2, 27%; and group 3, 51.2% ( p = 0.007). Pre-thaw morphologic grading and morphokinetic scores of the study groups did not reveal differences. p -values were 0.17 for the pre-thaw morphologic score, 0.54 for KID3, and 0.37 for KID5. The patients' demographic and clinical data were similar. The clinical pregnancy rate correlated with the degree of thawed blastocyst re-expansion measured 2 h after incubation. This standardized measure is suggested as a tool to predict the potential of treatment success before embryo transfer.