A time-lapse system was used to study the timing and coordination of events during early development from zygote to cleavage stage embryo. The aim was to identify markers linked to good-quality embryos and implantation. A total of 102 fertilized oocytes were followed for 20-24 h. Events such as appearance and disappearance of (pro)nuclei and timing and synchronization of cell cleavage were logged as time points after fertilization. Averages for these events and their synchrony were calculated and linked with fertilization method, embryo quality and implantation success. Fertilized oocytes that developed into > or =4-cell embryos had an earlier pronuclei disappearance and first cleavage than those that developed to 3- or 2-cell embryos. Intracytoplasmic sperm injection-fertilized 4-cell embryos spent a significantly shorter period as 2-cell compared with IVF-fertilized embryos (P = 0.0090). Development in the time-lapse system was similar to their siblings cultured in normal incubators, suggesting that the data from the time-lapse system can be extrapolated to the clinic's laboratory setting. Early disappearance of pronuclei and onset of first cleavage after fertilization was correlated with a higher number of blastomeres on day 2 after oocyte retrieval. In addition, synchrony in appearance of nuclei after the first cleavage was significantly associated with pregnancy success (P < 0.05).