Purpose The aim of this study was to (1) investigate the incidence of embryos derived from Bunfertilized oocytes^i.e., oocytes not displaying pronuclei (0PN) at the time of the fertilization check and (2) determine the clinical pregnancy rates when transferring 0PN-derived embryos. Methods In this retrospective study, 4424 IVF-ET cycles were reviewed. Results In total, 11.3 % (4966/43,949) 0PN-derived embryos were observed. It was found that female age, number of oocytes, and the top-quality embryo rate were significantly correlated with 0PN-derived embryo occurrence. The source of embryos transferred did not impact significantly on clinical pregnancy and livebirth rates. Of the 183 cycles included in this study where 275 0PN-derived embryos were transferred in total, only 0PN-derived embryos were available in 70 of those cycles. It was noteworthy that 13 healthy infants resulted from 0PN-derived embryos with an implantation rate of 17.0 %. Conclusion These results indicate that the traditional method of excluding embryos because of those oocytes originally lacking any sign of a pronucleus at the fertilization check should be reconsidered as transferring 0PN-derived embryos with subsequent expected developmental performance may be considered as an option for those patients where no other embryos are available.Keywords Abnormal fertilization . Pronucleus . 0PN . Pregnancy . ImplantationIn in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) treatment cycles, a fertilization check is performed at 17-20 h post insemination to exclude oocytes that have fertilized abnormally or not fertilized at all. Normal fertilization of an oocyte is defined by observing two distinct pronuclei (2PN) and two polar bodies after insemination. Oocytes showing no pronucleus (0PN), one pronucleus (1PN), or three pronuclei (3PN) (or more) are deemed as having fertilized abnormally and may be discarded. However, this assumption may not always be accurate. On the one hand, cytogenetic analysis has revealed that a proportion of diploid embryos can develop from 1PN zygotes [1]. Healthy babies developing from such embryos have been reported [2]. On the other hand, 2PN zygotes are not necessarily euploid. Furthermore, there are reports of 0PN-derived embryos present in 12 to 20 % of day 3 embryos [3][4][5] which result in healthy babies [4,6,7]. Although to transfer such embryos in the absence of the signs of normal fertilization may have become an option in clinical policy, it is still a dilemma for the clinical team when it comes to carrying this out in practice.In this study, fertilization results from conventional IVF were reviewed to (1) investigate the incidence of embryos derived from 0PN oocytes and (2) determine the clinical pregnancy rates (CPR) when transferring such 0PN embryos.