Blastocyst Questions

  1. What is a blastocyst?

  2. How big is a blastocyst?

  3. What is the primary source of blastocysts for research?

  4. When were early stem cells first isolated from IVF-blastocysts?

  5. How many unused embryos are stored in fertility clinics in the United States?



1. What is a blastocyst?

A blastocyst is a thin-walled hollow sphere made up of an outer layer of cells that will form the placenta, a fluid filled cavity and an inner cell mass containing cells that will form the embryo. The blastocyst develops after cleavage (e.g. cell division) of the fertilized egg and prior to implantation at approximately five days. 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.

2. How big is a blastocyst?

A blastocyst is a microscopic group of 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.

3.  What is the primary source of blastocysts for research?

Five-day-old eggs 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 fertilized eggs can be donated for research purposes by consenting donors, rather than being discarded.

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4.  When were early 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 .

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5. How many unused embryos are stored in fertility clinics in the United States?

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 are successful in having the children they want or because treatment is unsuccessful). According to the study, about two percent of these excess embryos are offered by the parents for adoption to create pregnancies in biologically unrelated mothers. Many parents are uncomfortable and unwilling to offer their excess embryos for adoption and would prefer to simply discard these embryos or to donate them for medical research that could help people. The bottom line is that there is no conflict between the adoption of embryos by biologically unrelated parents and the use of embryos for medical research: if all of the parents who prefer to put their excess embryos up for adoption do so, and all of the parents who prefer to donate their excess embryos for medical research do so, there would be more than enough embryos for both purposes.

 

 



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