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I have recently experienced a failure to fertilize in a few cases in a clinical IVF lab. In these cases, the eggs have been processed for ICSI. 16 hrs following injection there was no consistent sign of fertilization. In some cases, no pronuclei were observed but the second polar body was present. At 24 hrs there faint structures appeared but fertilization was questionable.  At 40 hrs pronuclei were present in all oocytes but instead there were multiple nuclei ranging from 3 or more.  One oocyte appeared to have what looked like 15 micronuclei.  All zygotes failed to cleave.  

The incidents occurred on separate days. We have checked microscope stage, dry bath and incubator temperatures, incubator pH and CO2 concentrations and media and all appear to be OK and passed internal QC. We have also checked medication lots used for stimulation and there is no apparent pattern.  Other cases on that fertilized on prior days all developed normally.    

Has anyone experienced a similar incident? Was it tied to microtubule development? 

What could be the cause? Any additional thought or comments would be appreciated.