How Many Frozen Human Embryos Are Available for Research?

Frozen human embryos have recently become the focus of considerable media attention. Frozen embryos are a potential source of embryonic stem cells, which can replicate themselves and develop into specialized cells (e.g., blood cells or nerve cells). Researchers believe that such cells might be capable of growing replacement tissues that could be used to treat people suffering from a number of diseases, including cancer, Alzheimer's disease, and diabetes. Among the most contentious issues in the stem cell debate are whether frozen embryos should be used to produce stem cells for research purposes and whether it is appropriate to use federal funds for research involving human embryos.

Many of the proposed resolutions to the embryonic stem cell debate are based on assumptions about the total number of frozen human embryos in the United States and the percentage of that total that is available for research. Accurate data on these issues, however, have not been available. Guesses on the total number of embryos have ranged wildly from tens of thousands to several hundred thousand.

RAND researchers Gail L. Zellman and C. Christine Fair, together with the Society of Assisted Reproductive Technology (SART) Working Group led by David Hoffman, MD, have completed a project designed to inform the policy debate by providing accurate data on the number of frozen embryos in the United States and how many of those embryos are available for research purposes. Their findings include the following:

Vast Majority of Frozen Embryos Are Held for Family Building

The practice of freezing embryos dates back to the first infertility treatments in the mid-1980s. The process of in vitro fertilization often produces more embryos than can be used at one time. In the United States, the decision about what to do with the extra embryos rests with the patients who produced them.

The RAND-SART team designed and implemented a survey to determine the number and current disposition of embryos frozen and stored since the mid-1980s at fertility clinics in the United States and the number of those embryos designated for research. The survey was sent to all 430 assisted reproductive technology facilities in the United States, 340 of which responded. Estimates for nonresponding clinics were developed using a statistical formula based on a clinic's size and other characteristics. The results show that as of April 11, 2002, a total of 396,526 embryos have been placed in storage in the United States. This number is higher than expected; previous estimates have ranged from 30,000 to 200,000.

Although the total number of frozen embryos is large, the RAND-SART survey found that only a small percentage of these embryos have been designated for research use. As the figure illustrates, the vast majority of stored embryos (88.2 percent) are being held for family building, with just 2.8 percent of the total (11,000) designated for research. Of the remaining embryos, 2.3 percent are awaiting donation to another patient, 2.2 percent are designated to be discarded, and 4.5 percent are held in storage for other reasons, including lost contact with a patient, patient death, abandonment, and divorce.

Embryos Available for Research Do Not Have High Development Potential

Although the 11,000 embryos designated for research might seem like a large number, the actual number of embryos that might be converted into stem cell lines is likely to be substantially lower. Because assisted reproductive technology clinics generally transfer the best-quality embryos to the patient during treatment cycles, the remaining embryos available to be frozen are not always of the highest quality. (High-quality embryos are those that grow at normal rates.) In addition, some of the frozen embryos have been in storage for many years, and at the time that some of those embryos were created, laboratory cultures were not as conducive to preserving embryos as they are today. Some embryos would also be lost in the freeze-and-thaw process itself.

To illustrate how such laboratory conditions might limit the number of embryos available for research, the RAND-SART team performed a series of calculations. Drawing upon the few published studies in this area, they estimated that only about 65 percent of the approximately 11,000 embryos would survive the freeze-and-thaw process, resulting in 7,334 embryos. Of those, about 25 percent (1,834 embryos) would likely be able to survive the initial stages of development to the blastocyst stage (a blastocyst is an embryo that has developed for at least five days). Even fewer could be successfully converted into embryonic stem cell lines. For example, researchers at the University of Wisconsin needed 18 blastocysts to create five embryonic stem cell lines, while researchers at The Jones Institute used 40 blastocysts to create three lines.

Using a conservative estimate between the two conversion rates from blastocyst to stem cells noted above (27 percent and 7.5 percent), the research team calculated that about 275 embryonic stem cell lines could be created from the total number of embryos available for research.^[1] Even this number is probably an overestimate because it assumes that all the embryos designated for research in the United States would be used to create stem cell lines, which is highly unlikely.

Conclusion

The RAND-SART survey found that almost twice as many frozen embryos exist in the United States as the highest previous estimate. Only a small percentage of these embryos are available for research because the vast majority are reserved for family building. Among those that are in principle available for research, some have been in storage for more than a decade and were frozen using techniques that are less effective than those that are currently available.

RAND research briefs summarize research that has been more fully documented elsewhere. This brief summarizes RAND-SART research reported in the following article: Hoffman DI, Zellman GL, Fair CC, Mayer JF, Zeitz, JG, Gibbons WE, and Turner TG. May 2003. Cryopreserved Embryos in the United States and Their Availability for Research. Fertility and Sterility 79 (5): 1063-1069.

RAND's Law & Health Initiative brings together policy researchers with expertise in civil justice and health care issues to analyze the resolution of health care disputes and the effects of law and litigation on health care quality, cost, and access. Law & Health materials are available online at http://www.rand.org/icj/ and http://www.rand.org/health/. RAND is a nonprofit institution that helps improve policy and decisionmaking through research and analysis. RAND® is a registered trademark.

The fact is that embryos are available for stem cell research in this country, and no law prohibits that.

If all the activists on that side of the question would pony up and provide embryos, there would be millions of them.

But they'd prefer this to be a political question rather than a scientific or medical question.

Actually doing the research isn't the goal. The goal is getting you to concur that some of your paycheck should be used by the government to kill and harvest embryos for stem cells.

There is no law against embryonic stem cell research. The law restricts government funding, not private. The dems and the msm are going to win this, just like they will with the war in Iraq or global warming being caused by humans. Repeat a lie often enough and it becomes reality. In politics and almost every other area of life, perception is everything.

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The left has plenty of embryos to butcher and carry out their junk science on. The fact is that they know it's a dead end, they just want federal funding to provide "hope" and add a further safeguard to abortion.

I'm all for getting the government out of the business funding things it has no business being involved in, but as long as my tax dollars are being used for politically/religious based things I don't agree with (think "abstinence programs" in public schools, and the whole business of regulating and licensing marriages), then I want your tax dollars used for things you don't agree with which I DO agree with. The government will keep getting bigger and bigger until all the various groups of citizens stop demanding tax dollars for their own pet programs.

This article has a sort of off-point focus, though. There's no shortage of embryos at least as far as current research needs are concerned, but there's a shortage of funding because federal research funds are being diverted away from embryonic stem cell research. Again, I'm not in favor of federal (or state) funding of this or any other medical research outside of what's critical to true public health and national security issues. But as long as the government is dipping into my pockets for money to hand out to a laundry list research areas, I don't want it selectively diverting its funding away from reserach that I'm supportive of.

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