Belgian scientists reported that they could split 4-cell human embryos into individual cells and get complete embryos from each individual cell. In a talk at the European Society of Human Reproduction and Embryology meeting, they described the experiment:

Three, good quality 4-cell stage embryos were split into 12 single blastomeres and allowed to grow in vitro to produce twelve morulas that were cultured in the conventional way for hESC derivation. From these twelve, one resulted in a stable hESC line.

They say this means that each cell at the 4-cell stage is equivalent; their next step is to see if they can get four hESC lines from a single 4-cell embryo. They do note that, "We need to determine whether the removal of one cell at the 4-cell stage impairs the capacity of the embryo to develop into a healthy child."

Interestingly, the result is billed as a technique that "may lessen ethical concerns". Apparently they mean that manipulating an embryo earlier in his/her life is better, assuming the 3-cell embryo can proceed to develop normally. But their results also point out that the single cell removed is totipotent, able to form a complete embryo on its own. This just multiplies the ethical problems rather than lessens them.