June 21 (HealthDay News) -- About half the patients being treated at U.S. fertility clinics say they'd be willing to donate their unused embryos for stem cell research, a new survey reports.

The findings, released Wednesday by the journal Science, mean that up to 10 times as many embryos would be available for research than previously estimated, should U.S. legislators ever permit their wider use.

However, such a move also became less of a possibility on Wednesday, after President Bush for the second time vetoed a bill that would have loosened federal restrictions on funding for embryonic stem cell research.

Reacting to the study findings, co-researcher Dr. Anne Drapkin Lyerly, of Duke University, said, "We were surprised. These were quite dramatic findings."

"When we asked these infertility patients about what they thought they would do with embryos, 50 percent said that they would be likely to donate some or all of them for research, and 60 percent said that they would be likely to donate them for stem cell research," added Lyerly, an associate professor of obstetrics and gynecology at Duke University and core faculty at Duke's Trent Center for Bioethics, Humanities and History of Medicine.

"This is a dramatic increase in what we might estimate as the number of embryos available for research purposes," she said.

The other study author was Ruth Faden, director of the Johns Hopkins Berman Institute of Bioethnics. The study will also be published in the July 6 print edition of Science.

If only 25 percent of the 400,000 frozen embryos thought to be stored in the United States were donated, that would give scientists 100,000 embryos (vs. 11,000 previously estimated), resulting in 2,000 to 3,000 viable stem cell lines.

In addition, the authors pointed out, the paper adds an important new voice to the chorus surrounding stem cell research.

"We understand the perspective of lawmakers, advocates, etcetera, but we really didn't know what the preferences of infertility patients were or what animated their decisions," Lyerly said. "We wanted to bring their voices into the national debate and also try to understand how these decisions were made."

"We understood that infertility patients were facing a very difficult moral decision about what to do with excess embryos left over after infertility treatment, and these are the people who have interfaced most intimately with moral decision-making around embryos. Yet their perspectives are really absent from national debate," she continued.

Embryonic stem cells are pluripotent, meaning they have the ability to develop into virtually any cell type in the body. The hope is that these cells may one day yield treatments or cures for diseases such as diabetes, liver failure, spinal injury, stroke, Alzheimer's disease and heart disease.

However, harvesting stem cells involves destroying a viable embryo, a practice many Americans object to on moral grounds. Embryonic stem cell research in the United States has been severely limited since August 2001, when Bush placed limits on federal funding of the field. Now, federal funds can only be used to study stem cell lines derived from embryos that had been destroyed before that date.

The bill recently passed by the Democratic-led Congress and now vetoed by Bush sought to lift that restriction. News sources on Wednesday reported that the Democrats do not have enough votes to override a veto.

The Science paper was based on a 12-page survey completed by more than 1,000 patients at nine U.S. fertility centers that had created and frozen embryos as part of fertility treatment.

Almost half (49 percent) of the respondents said they would be likely to donate some or all of their excess embryos to research in general.

That number increased to 60 percent when the question referred specifically to stem cell research and research aimed at developing treatments for human disease or infertility.

Other options, such as having the embryos destroyed or donating them to another infertile couple, seemed less attractive.

The results are in accord with the sentiments of the majority of the American public, the researchers said.

And reproductive specialists agreed.

Commenting on both the new study and the Bush veto, Dr. Steven Ory, president of the American Society for Reproductive Medicine, said in a prepared statement, "Our patients have been following the progress of embryonic stem cell research over the last few years . . . They understand that ESC research in this country is being slowed by the lack of good stem cell lines and they want to help."

He added, "The legislation that recently passed both the House and Senate would have allowed federal funding for research using new embryonic stem cell lines but would not fund the derivation of these lines. It is disappointing that the President did not consider that -- and the fact that former infertility patients very much want to contribute their embryos to scientific research with the potential to heal millions."

Dr. David Grainger, president of the Society for Assisted Reproductive Technology, added, "The Duke-Hopkins survey in Science shows that patients who have overcome infertility using assisted reproductive technology have thought long and hard about what they want to do with their unused, stored embryos. . . Patients' decisions about the use of their embryos should be respected, and patients deserve to have the opportunity to follow through with their decisions.

Lyerly and Faden plan to publish more findings from the survey in subsequent papers.

"My hope is that the perspectives of the infertility patients who have legal authority and moral responsibility for the embryos will be represented in the national debate," Lyerly said.

SOURCES: Anne Drapkin Lyerly, M.D., associate professor, obstetrics and gynecology and core faculty, Trent Center for Bioethics, Humanities and History of Medicine, Duke University, Durham, N.C.; June 20, 2007, prepared statement, Steven Ory, M.D., president, American Society for Reproductive Medicine, and David Grainger, MD, MPH, president, Society for Assisted Reproductive Technology; early online release, June 20, 2007, and July 6, 2007, print edition, Science