A greater insight into the molecular basis of blastocyst competency for implantation might help to improve pregnancy rates in human IVF programs. Implications for human fertility. From the results ...

Once removed from the blastocyst they lack the outer trophoblast ... be "nudged" into becoming any cell type found in the human body. These are the cells that Thomson used in his research.

Early zygote and blastocyst donations from patients of IVF clinics have helped shed light on this black box period of development, but human embryos are a limited resource and ethical concerns ...