The trouble with embryos.

In an effort to quell ongoing debate about the ethics of human embryonic stem cell (hESC) research, there have been concerted efforts to develop ethical standards for both embryo and hESC research and to entrench these standards in law. Surprisingly these efforts have not included efforts at standardizing the meaning of the pivotal term 'embryo'. This paper reviews the legal framework for embryo research in the United Kingdom, the United States and Germany and highlights the absence of any agreed upon standard for what counts as a human embryo. This is an important lacuna, especially in light of the most recent advances in stem cell research involving the reprogramming of human somatic cell nuclei to generate human induced pluripotent stem (iPS) cells. [ABSTRACT FROM AUTHOR]