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Background: Cleavage stage multinucleation is a morphological assessment IVF labs may use to rank embryos for transfer, as blastocysts that were multinucleated at the 2-cell or 4-cell stage have a lower live birth rate (LBR) compared to blastocysts that were mononucleated1. However, when these blastocysts are PGT-A tested, the euploidy rate is similar2, indicating that the poorer pregnancy outcomes may not be due to aneuploidy. It is unknown if multinucleation is indicative of a lower likelihood of pregnancy for euploid blastocysts. Aim: To determine if LBR following transfer of euploid blastocysts is lower when blastocysts were multinucleated at the 2-cell or 4-cell stages. Method: Retrospective study on 360 euploid blastocysts cultured in the EmbryoScope or EmbryoScope+ between March 2018 and October 2019, and individually transferred. Time-lapse images were retrospectively assessed for multinucleation at the 2-cell and 4-cell stage. A multinucleated embryo was defined as having [Formula: see text] 1 cell with [Formula: see text] 2 nuclei. Results: Blastocysts that were multinucleated at the 2-cell stage (n=139) had a similar LBR to mononucleated embryos (40.3% vs 41.6%). Multinucleation at the 4-cell stage (n=43) also did not significantly affect LBR (37.2% vs 43.6%). Multivariate logistic regression analysis found no significant effect of multinucleation on LBR. Biochemical pregnancy, clinical pregnancy (fetal heart), and miscarriage rates were also similar between multinucleated and mononucleated embryos. Conclusion: This study found no evidence that multinucleation at the 2-cell or 4-cell stage influences pregnancy rate in euploid blastocysts. As such, the assessment of cleavage stage multinucleation for PGT-A tested embryos may not be useful in ranking PGT-A tested embryos for transfer. Further work is required with larger numbers of embryos to confirm how the degree of multinucleation may influence LBR.