To evaluate spontaneous embryo hatching in an endometrial epithelial coculture system, and compare it with cases where coculture was performed because of maternal age, previous repeated implantation failures, or both. To clarify in which cases assisted hatching would be appropriate.Individual human embryos were cocultured on an endometrial epithelial cell monolayer until Day 6.Blastocyst hatching rate at Day 6, depending on maternal age, was 9.1% (age or = 37 years). However, blastocyst hatching rates depending on number of previous IVF failures were similar.Maternal age and previous implantation failures are factors affecting the ability of human embryos to reach the blastocyst stage in coculture. However, assisted hatching is not justified in these populations because of the absence of hatching rate differences between blastocysts obtained from these two groups and the control group.