There is no way to prove that an arrested embryo would have stopped growing if it had been put into a woman's womb rather than a lab dish, said Robin Lovell-Badge of the Medical Research Council's National Institute for Medical Research in London. So that leaves open the possibility that it was the lab conditions that halted their growth, he said.
The Rev. Tad Pacholczyk, director of education for the National Catholic Bioethics Center in Philadelphia, said he believed an embryo may not be dead if individual cells are still alive and able to create stem cell lines.
Landry says an embryo is dead if its cells irreversibly stop working together to function as a single organism. But even under that definition, Pacholczyk said, scientists know too little about early embryos to discern when one is truly dead.
Dr. George Daley of the Harvard Stem Cell Institute said the new paper's approach also raises a scientific concern: Stem cells from arrested embryos might carry the risk of some undetected defect.
"If there was something wrong with the embryo that made it arrest, isn't there something wrong with these cells?" that could cause problems with their use, he asked. "We don't know."
