The Legend of the 400,000 Embryos

Date: 06/11/2004

That there are 400,000 frozen human embryos that could provide a potentially unlimited supply of stem cells has become a truism of the stem cell debate. Indeed, in recent letters to President Bush, members of both the House and Senate explicitly refer to these 400,000 frozen embryos in urging the administration to change its current policy on embryonic stem cell research (ESCR).

A further truism is that the stem cells lines that could be derived from these frozen embryos have the potential to cure numerous diseases, but that such cures remain just around the corner and just out of reach because the Administration refuses to fund research in which these embryos would be destroyed. After all, yet another truism goes, the vast majority of these embryos will likely be destroyed anyway. Because the number of frozen embryos is so large there is an underlying assumption, accepted almost without question, that an equally large number of therapeutic stem cells can be derived from them.

But like all such truisms, there is little truth behind these assumptions:

  • According to a 2002 survey by the RAND Corporation of IVF clinics in the United States , the vast majority of the 400,000 currently frozen embryos are NOT slated for destruction. The vast majority–88.2%–are being held for family building.
  • Only a small fraction–2.2% — are slated to be discarded.
  • An only slight higher percentage –- 2.8%–have been designated for research. That means of the original 400,000 frozen embryos, only 11,000 are actually available to be destroyed for their stem cells.
  • Only a small number of those 11,000 embryos would actual yield stem cells. Using what it calls “a conservative estimate” the RAND study calculated that only about 275 stem cell lines could actually be developed from the embryos available for research. And even then, the RAND study concedes that this number “is probably an overestimate.”

Leading fertility experts also agree that frozen embryos would yield a far smaller number of stem cell lines than is often assumed. Dr. William Gibbons, of the Jones Institute for Reproductive Medicine in Virginia, says the Institute has about 200 frozen embryos available for research, but “there is no guarantee that we would get any stem cells from those 200 frozen embryos. We hear all this stuff about how all these embryos are available, but we just didn’t think there was much there.” And Dr. Barry Behr of Stanford University notes that “By far, by far, the vast majority of embryos that are frozen are not good. If we thawed 10,000 embryos, we would get 100 or so that are viable blastocysts”.

So behind the seemingly impressive number of “400,000 frozen embryos,” the reality is that the actual number of stem cell lines likely to be produced from them is so small as to be clinically useless. In order to treat diseases (still a very distant prospect using human embryonic stem cells) hundreds of thousands more embryos, beyond those currently frozen and available for research, would be needed. This could only be achieved by a deliberate effort to create new embryos for the sole purpose of destroying them–an outcome that the use of the frozen embryos is supposed to avoid, but would most likely cause.

And if these 275 potential stem cell lines derived from frozen embryos would therefore be used only in basic research, then the number of human embryonic stem cell lines already available for federal funding under current administration policy (a number sure to increase) is already sufficient for this purpose.