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Blastocyst Questions1. What is a blastocyst? A blastocyst is a microscopic thin-walled hollow sphere made up of an outer layer of cells that would form the placenta, a fluid filled cavity, and an inner cell mass containing cells that would form the embryo. The blastocyst develops about five days after the egg is fertilized, after cleavage (e.g. cell division) and prior to implantation. Further development occurs only if the blastocyst implants successfully in a uterus. In other words, the blastocyst cannot live on its own; it can only become a viable embryo if it is implanted in a woman's womb. A blastocyst is a microscopic group of about 150 cells — smaller than Roosevelt's eye on the face of a U.S. dime. At day five after fertilization, when stem cells can be harvested, a blastocyst is approximately 0.1 to 0.2 millimeters (0.0039 to 0.0079 inches) in size – about the size of the period at the end of this sentence. 3. What is the primary source of blastocysts for research? Microscopic five-day-old embryos fertilized in a laboratory dish in an in vitro fertilization (IVF) clinic, prior to implantation, are the primary source of blastocysts for use in stem cell research. Once they are no longer needed for reproductive purposes, these embryos can be donated for research purposes by consenting donors, rather than being discarded. People who have difficulty conceiving a child sometimes go to fertility clinics for help. During IVF, eggs are removed from the woman's body and fertilized with sperm in a culture dish. After some of the fertilized eggs develop into blastocysts, one or more of the most healthy blastocysts are placed in the woman's uterus. If a blastocyst implants in the wall of the uterus and continues to develop, it can result in a normal pregnancy. Additional blastocysts can be frozen for later use, or discarded because they are of unsuitable quality for implantation. Blastocysts that are of unsuitable quality or no longer needed for fertility treatment can be donated by the parents for research rather than being discarded. There are many leftover embryos because IVF clinics fertilize as many eggs as they can from the donor couple. But some of those fertilized eggs develop abnormally or are found to carry genetic defects that cause serious diseases. Only blastocysts that appear most healthy are implanted in the mother's womb in an attempt at pregnancy. Others that appear normal may be frozen for subsequent attempts. Embryos that cannot be implanted because of abnormal development or serious genetic defects, as well as frozen embryos that are no longer needed for fertility treatment can be donated by parents and used by scientists to derive embryonic stem cell lines. Scientists may only use the blastocysts after they have already been slated for disposal, and only with the informed consent of the donors. 4. When were stem cells first isolated from IVF blastocysts? In 1998, Wisconsin researcher Dr. James Thomson first published the method for keeping human embryonic stem cells alive and in an unchanged state — meaning they weren't transforming themselves into heart cells, liver cells or other specialized cell types. For more information on Dr. Thomson's research please visit his web site at the University of Wisconsin. 5. How many unused embryos are stored in fertility clinics in the United States and what happens to them? Embryos that are not immediately used for fertility treatments are often frozen by fertility clinics for potential future use. According to a survey conducted by Rand Health in 2003, there are approximately 400,000 such embryos in storage in the United States. (Source: Hoffman, D.I., et al. 2003. Cryopreserved Embryos in the United States and Their Availability for Research. Fertility and Sterility 79: 1063-1069.) Most of these embryos will never be used for fertility treatment either because the parents were successful in having the children they want or because treatment is unsuccessful. In addition to donating unused embryos for research, discarding them or leaving them frozen, there is one more alternative: According to the Rand study, about 2 percent of excess embryos are offered by the parents for adoption to create pregnancies in biologically unrelated mothers. But many parents are uncomfortable and unwilling to offer their excess embryos for adoption. The bottom line is that there is no conflict between the adoption of embryos and the use of embryos for medical research. There are more than enough embryos for both purposes. |
Basic Questions
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