WASHINGTON — If scientists want to develop new supplies of embryonic stem cells, they may have to take the bold and controversial step of creating human embryos expressly for research, many leading fertility experts say.
Tens of thousands of embryos are frozen at fertility centers, and a widespread assumption in the debate over stem-cell research has been that scientists can use them.
But in clinics around the country, embryologists and doctors tell the same story: Almost every embryo is spoken for. The vast majority of couples use their frozen embryos, or plan to use them, in attempts at pregnancy. It may be that embryos will become available if there are concerted efforts to encourage couples to donate them. But so far, few couples have agreed to do so.
An alternative, creating human embryos and nurturing them solely for experiments that will destroy them, leaves even many supporters of the research deeply uneasy.
The harsh truth about the status of the frozen embryos "changes the debate," said Dr. Thomas Pool, scientific director of the Fertility Center of San Antonio, Texas. If the embryos already existed, were unwanted byproducts of in vitro fertilization, and were never going to be used to make babies, Pool said, people could ask, "Could I save them and do some good with them?" That was "a warm and fuzzy way for people to get around the question of making them," he added. "It's an easy way to not have to come back to the salient question: What are these things that we make in IVF labs?"
This conundrum does not arise in the area where President Bush has proposed allowing federally financed research. He would permit work to go ahead on existing lines of stem cells — Bush says there are 60 lines, while others say there may be as few as a dozen usable ones.
Rather, the issue comes up when scientists try to develop new stem cells, abroad or with private money. Some say this is necessary because the existing lines are insufficient and may not be safe for human use.
Even if scientists did want to use frozen embryos at fertility centers, there would be hurdles to overcome, said Dr. William Gibbons, a reproductive endocrinologist at the Jones Institute for Reproductive Medicine of Eastern Virginia Medical School.
Each patient who has agreed to donate embryos must be contacted and agree to the particular stem-cell project. Then scientists must buck the odds in getting the embryos to grow and isolating stem cells from them.
Those odds can be long.
At the Jones Institute, about 200 embryos might be available for research according to forms signed by patients, but that might not be enough to generate any stem cells, Gibbons said.
"We hear all this stuff about how all these embryos are available," he said. "But we just didn't think there was much there."