ABSTRACT
Human embryos that are cultured in vitro sometimes have two or more nuclei visible within a single blastomere, even after apparently normal fertilization. This phenomenon, referred to as multinucleation, occurs after the completion of meiosis, and can be seen during interphase throughout the stages of in vitro culture. Multinucleated blastomeres (MNB) may be observed most readily on day 2 and 3 of development, but on day 3 definitive identification may be compromised by overlap between cells, compaction and/or fragmentation. Although multinucleation continues to occur through blastocyst development, it is very difficult to observe microscopically after day 3.1 A high incidence of multinucleation is associated with other types of embryo dysmorphism, including fragmentation, impaired embryo development and arrest,2-5 but it does not always correlate with poor embryo morphology.2,6
Consequently, care should be exercised when deciding the fate of multinucleated embryos (MNE) that are otherwise apparently of good quality. MNE do have the potential to implant, but their implantation and subsequent pregnancy rates are lower than those of non-MNE.4,7-10 Several studies have confirmed the birth of healthy babies that originated from MNE,4,8,10 and therefore, if no other embryos are available for transfer, it is preferable to transfer these embryos unless other developmental information such as the presence of chromosomal anomalies is known.
