OBJECTIVE: The time-lapse system in the EmbryoScope (ES) can be used for image acquisition of embryos and subsequent analysis of the exact timing of cell division events. The purpose of the study is to link successful implantation of embryos to the exact timing of cell division events by use of the ES. DESIGN: Retrospective analysis on embryos from ICSI cycles. MATERIALS AND METHODS: Included in the study were only transferred embryos with 100% implantation (where the number of gestational sacs confirmed by ultrasound match the number of transferred embryos); or embryos with 0% implantation, (where no biochemical pregnancy was achieved). Images of the embryos were acquired every 20 min during 70 hours in the ES. Subsequently the ES Viewer was used to identify the exact timing of PN formation and fading, and 1st, 2nd and 3rd division. The time of each event was recorded in hours after microinjection. Timing was classified in quartiles and grouped in two categories, the first category defined by the time-range of the two central quartiles, the second category “Out of range” includes the rest of the data. Implantation is compared between the categories by a Chi-square test. RESULTS:Table 1Implantation within the time-range for each variableEventPN formationPN fading∗1st division∗2nd division∗3rd division∗Range (h)7.8 - 11.122.3 - 25.824.4 - 28.235.3 - 40.636.0 - 41.6Implanted (%)2029.528.823.229.7N3247463747For the events marked with ∗ (PN fading, 1st, 2nd and 3rd division), there is a significant difference (p<0.05) between the relative abundance of 100% implantation and 0% implantation inside and outside the given time-range for the event. Open table in a new tab For the events marked with ∗ (PN fading, 1st, 2nd and 3rd division), there is a significant difference (p<0.05) between the relative abundance of 100% implantation and 0% implantation inside and outside the given time-range for the event. CONCLUSION: The timing of PN fading, 1st, 2nd and 3rd division can be significantly linked to successful embryo implantation. Although the amount of data is limited, the analysis shows that the ES has the potential of improving embryo selection through the exact determination of timing of embryo development events.