Multinucleation per se is not always sufficient as a marker of abnormality to decide against transferring human embryos

Objective: To assess the developmental competence of human embryos with multinucleation (MN). Design: Experimental study. Setting: Private fertility center. Patient(s): Forty-four couples donating 143 zygotes for confocal imaging study, and 78 couples included in the retrospective clinical study. Intervention(s): Time-lapse imaging study using confocal and light microscopes. Main Outcome Measure(s): Cytokinesis at first mitosis, MN, chromosomal behavior, euploidy, implantation, successful delivery of healthy baby. Result(s): About 25% of the embryos showed abnormal cytokinesis (n = 34). All showed MN, and their development was greatly impaired. More than 75% of embryos that showed normal cytokinesis at first mitosis displayed MN (n = 81). However, the subsequent development of embryos with MN was similar to that of embryos without MN in vitro and in vivo. Most blastocysts were euploid. All chromosomes in several MNs took part in forming a bipolar spindle after the nuclear envelope breakdown followed by normal cleavage and development to the blastocyst stage. The implantation potential of embryos with MN was similar to that of embryos without MN, and healthy babies were born from the former group after transfer. Conclusion(s): The presence of MN after the first mitosis does not adversely affect the subsequent development of embryos if they showed normal cytokinesis at this stage. The poor development of embryos with MN is mainly caused by abnormal first cytokinesis. (C) 2016 by American Society for Reproductive Medicine.