The detection of multinucleation was compared with time-lapse system and conventional control timing proposed by ESHRE consensus and its impact on pregnancy rate was researched. Retrospective study in an IVF Center. A total of 686 transferred embryos from 511 IVF-ICSI patients were assessed based on the time-lapse monitoring system. All embryos were evaluated with EmbryoScope (EmbryoScope Unisense FertiliTech, Denmark) for presence and persistence of multinucleation. All embryos were checked again via video review at ESHRE Concensus proposed embryo evaluating times (23±1h, 26±1h, 44±1h). 145 patients had multinucleated embryo transfer (group 1) and 366 patients had no multinucleated embryo transfer (group 2). There were no significant differences (p>0.05) in age, BMI, number of oocyte retrieved, number of IVF attempt, day 3 FSH, indication for IVF and frequency of single vs double embryo transfer between the groups. Group 1 have significantly lower clinical pregnancy rate (23.4% vs 44.0%, p>0.001) and lower implantation rate (23.3% vs 43.6%, p>0.001) compared to group 2. In multivariate analysis only patients age (p=0.001, OR=0.95 CI=(0.92-0.98)) and presence of multinucleation (p<0.001 OR=0.37, CI=(0.24-0.56)) were the only significant predictors of clinical pregnancy rate. Despite the importance of multinucleation, only 27.7% (44/159) of the embryos with multinucleation can be detected with conventional control timing of the embryos which was proposed by ESHRE consensus. The remaining 73.2% (115/159) embryos with multinucleation have duration of multinucleation out of the proposed embryo check time intervals. Multinucleation can not always be detected by conventional control timings. The time-lapse monitoring system is the only available tool to identify all cases with multinucleation which significantly decrease pregnancy rates.