Stem cell treatments have the potential to revolutionize medicine. It could be possible to develop stem cell–based treatments for chronic heart disease, Type I diabetes, and Parkinson’s disease, for example, and to use stem cells in the healing of spinal cord damage, the brain damage caused by a stroke, or the damage to heart muscles caused by a heart attack.
In California, in recognition of this potential, Proposition 71 set up a 10-year, $3 billion program to build facilities for stem cell studies and to fund research with the ultimate goal of helping to develop therapies based on stem cells.
This research, however, would require a steady supply of stem cells, particularly human embryonic stem cells. Those embryonic stem cells are collected from developing human embryos that are created from eggs—or oocytes—harvested from the ovaries of female donors.
The oocyte donation process is not without its risks to the donors, and the California Institute for Regenerative Medicine contracted with the National Academies to assemble a workshop that would bring together experts from various areas to address the questions of what is known about these risks, what needs to be known, and what can be done to minimize them. In response, the National Academies formed the Committee on Assessing the Medical Risks of Human Oocyte Donation for Stem Cell Research that held a workshop in San Francisco on September 28, 2006, devoted to those issues. This report is a summary and synthesis of that workshop.
The report summarizes the views expressed by workshop participants, and while the committee is responsible for the overall quality and accuracy of the report as a record of what transpired at the workshop, the views contained in the report are not necessarily those of the committee.
THE RISKS OF OVARIAN STIMULATION
In order to increase the number of eggs that can be retrieved from a single donor, the donor normally takes a regimen of hormone shots, that is, fertility drugs. These hormones will generally cause 10 to 20 eggs—instead of the usual single egg—to mature in the ovaries at the sametime. The drugs also have a variety of potential health effects, some minor and some potentially major.
The most prominent side effect of this ovarian stimulation is ovarian hyperstimulation syndrome (OHSS). Its symptoms include increased ovarian size; nausea and vomiting; increased permeability of the blood vessels, leading to an accumulation of fluid in the abdomen; breathing difficulties; hemoconcentration, or an increased concentration of red blood cells; kidney and liver problems; and, in the most severe cases, blood clots or kidney failure. Data from women taking fertility drugs in order to undergo in vitro fertilization (IVF) show that only a very small percentage—about 0.1 to 0.2 percent—experience what is classified as severe OHSS, and a much smaller percentage suffer truly dangerous complications. For example, about 1.4 of every 100,000 women undergoing an IVF cycle experience kidney failure.
The OHSS risks for egg donors are expected to be much lower than the OHSS risks calculated from women involved in IVF. The reason is that a large percentage of the severe complications of OHSS seen in IVF patients are linked to hormonal changes in a woman’s body that accompany pregnancy. Since oocyte donors do not get pregnant in the cycle in which they donate their eggs, they can be expected to have many fewer side effects than IVF patients.
There is also concern that the use of fertility drugs may lead to an increased risk of hormone-dependent cancers—in particular, breast, ovarian, and uterine (endometrial) cancers. Epidemiological studies of this issue must be interpreted carefully, because infertile women generally are at higher risk for these cancers than women in the general population, so the increased risk due to infertility must be separated from any possible increased risk caused by fertility drugs. The evidence to date is limited, but does not support a relationship between fertility drugs and an increased prevalence of breast or ovarian cancer. More research is required to examine what the long-term impact fertility drugs may be on breast and ovarian cancer prevalence rates. For uterine cancer, the numbers are too small to achieve statistical significance, but it is possible that fertility drugs may cause some increased risk of uterine cancer.
Questions have also been raised about the possible effects of ovarian stimulation on a woman’s long-term fertility. Presently there is no evidence, either from studies of women who have taken fertility drugs or from what is known about ovarian physiology, that ovarian stimulation may impact a women’s long-term fertility.
THE RISKS OF EGG RETRIEVAL SURGERY
Removing the mature eggs from a donor requires surgery—the insertion of an aspirating needle through the wall of the vagina and into the ovary—that is done under anesthesia. Both the surgery and the anesthesia carry certain risks.
Experience with IVF patients shows that the risks are low. One study of several hundred thousand surgeries found, for example, that only 0.002 percent of the women had complications that required surgery to correct. Complications due to infection are also rare and apparently can be avoided almost completely if proper aseptic techniques are used.
Ovarian torsion, in which an ovary twists around its supporting ligament and cuts off its blood supply, is another rare complication in women undergoing IVF. However, it is associated mainly with women who have become pregnant via IVF, so it should be even rarer among research oocyte donors.
In general, consideration of the risk factors for surgical complications—including previous surgeries, a history of pelvic inflammatory disease, endometriosis, and pelvic adhesions—implies that egg donors would be anticipated to have much lower risks from surgery than has been the experience with women undergoing IVF.
Similarly, the risks from anesthesia for oocyte donors should be very low. Anesthesia in general is very safe today, with deaths occurring once in 200,000 to 300,000 cases. It should be even safer for donors, because few of the factors that increase the risks of anesthesia apply to them.
Finally, there are no data to suggest that egg retrieval surgery poses any risk to a woman’s future fertility.
THE PSYCHOLOGICAL RISKS OF OOCYTE DONATION
The psychological risks for egg donation for research may differ from donation for reproduction, primarily because of different motivat-
ing factors for donation and different end uses of the donated eggs. When a woman chooses to donate her eggs for use in IVF or scientific research, it is a very personal decision, one with a variety of psychological implications and consequences. The psychological risks fall into three categories: issues associated with the screening process, problems surrounding the donation procedure itself, and the post-donation adjustment to the donation.
The main risk in the first category is that the screening process may reveal some previously unknown psychological or medical condition that disqualifies the woman from donating. This can be uncomfortable or psychologically threatening to the applicant.
During the donation process itself, some women report mood swings and irritability caused by the fertility drugs, pain caused by the injection, and anxiety in anticipation of the surgical procedure. The issues generally disappear after the procedure is complete.
Finally, after the donation, the main psychological issues are related to worries about future fertility and concerns about children conceived from the eggs. The latter will not be an issue for research donors, and the former is best dealt with by having more and better research done about the risks of oocyte donation, so that donors will have a realistic assessment of the risks associated with their donation.
DIRECTIONS FOR THE FUTURE
One of the most striking facts about in vitro fertilization is just how little is known with certainty about the long-term health outcomes for the women who undergo the procedure. There are no registries that track the health of the people who have taken part in IVF, and much of what is known about the risks for women participating in IVF may not be directly applicable to oocyte donors. Research donors, for example, are likely to be drawn from a much broader range of women than IVF patients, who tend to be primarily Caucasian women in middle to upper socioeconomic groups.
Thus it will be important in the coming years to accumulate extensive health data for women whose eggs are harvested and to monitor them for long-term effects. With more data it will be possible to quantify the various risks of oocyte donation much better than can be done today and to put numbers to the risks that a donor may face.
One of the most important challenges facing those collecting oocytes for research will be to minimize the risks for donors. Two strategies will be particularly important in this effort. The first is to identify, through a screening process, which potential donors have particular medical and psychological risk factors and to exclude them from the donor pool, since their risk for complications is higher than normal. The second is to tailor the donation process to the individual patient, modifying the procedures as necessary to keep each patient’s risks to a minimum. For example, it is possible to minimize the risk of OHSS by monitoring the number of eggs maturing in a woman’s ovary and then modifying the hormone treatment accordingly, so that she does not develop too many eggs at one time.
Finally, it makes sense to look for alternative sources of oocytes that do not depend on putting women volunteers through ovarian stimulation and retrieval surgery. It may be possible, for example, to develop ways to bring immature and partially mature eggs to maturity in vitro, which would increase the number of available oocytes without increasing the number of donors. Or, with the development of the proper retrieval and storage techniques, it might be possible to retrieve oocytes from cadavers in much the same way that organs are retrieved from the bodies of people who have signed organ donation cards. At this point, it is uncertain how many oocytes may ultimately be available from such alternative sources.