I'm not an expert, but I think there are three different types of stem cells.
The media just focus on the ones from fetuses
I am. Or was. If I can remember stuff from 15 years ago I should explain a little bit about stem cells so that people understand. These are undifferentiated cells with the potential of being able to turn into any cell in the body. When a spermatocyte breaches the cell membrane of an oocyte the nuclear material of the haploid cells (these only have 23 chromosomes instead of the paired 46 in a diploid cell), through a series of events, are able to come in contact with each other. This is the moment of fertilization and now the zygote has the “potential” to develop into a human being. The zygote then begins to divide, and the clump of undifferentiated cells becomes what we call a blastula. At this point, if we were to take some really really really small tweezers and separate each cell of the blastula/blastocyst and grew them individually, each one could turn into a human being; more-or-less a clone of the others. THESE are embryonic stem cells and are by definition “Pluripotent;” can turn into anything. As the blastocyst grows the cells then start to differentiate; become destined to perform a job. For example some of the first cells to break off and differentiate are called trophoblasts, and these turn into first, a cell layer than nourishes the developing embryo, and eventually becomes the placenta, amniotic sac, and umbilical cord. There is some kind of poorly understood (at least to me) chemical signal that is sent to tell these cells that tells them they have a job to do, and their form is forever changed to serve their function. Yes, after fertilization each cell has all the same genetic material as the others (we won't get into mitochondrial DNA) but all that info is not necessarily accessible. Only in the stem cell stage can the entire genome be potentially accessed.
So now we have a trophoblast (differentiated cells) and a blastocyst (undifferentiated cells that will turn into the embryo). More and more cells break off from the blastocyst and are transformed into precursors of organs and tissue. However the body keeps a store of these undifferentiated cells so it can turn them into whatever they want. As the embryo grows the percentage of stem cells becomes less and less, but they can even be found in the bone marrow adults. For reasons that I do not understand (but some people may) the stem cells found in adult bone marrow are not easy to induce. It could be that what we once THOUGHT were stem cells in the bone marrow are not really stem cells at all, but minimally differentiated cells that are destined only to make different kinds of blood cells. Scientists now call them somatic stem cells, or adult stem cells.
The cells we want to use when treating neurologic diseases are embryonic stem cells as we want them to be able to change into new nerve cells. The way we obtain them is to interrupt cell division at the blastocyst stage and then grow the cells in a culture.
Now the question is whether or not stem cells in the fetal blood (umbilical cord blood) are somatic or embryonic. I have always been under the impression that they are somatic and cannot be used in the way described in the previous posts. They can be used to make blood products but not nerve cells. I may be wrong and there may now be ways to do this but the reason I doubt it is that if cells are allowed to clump together to form embryoid bodies, they begin to differentiate spontaneously. It seems that if they are present in blood in any appreciable quantity then they should clump (and we’d be popping babies out of our veins!!). I will have to look into this though as I have not picked up a book on the topic since 1986.
So, while we are taking these stem cells at the blastocyst stage we are NOT killing a living being any more than we are if we eat a sunflower seed or a tomato. No brain has developed. No nerve cells have even developed. If we wait longer until the embryo develops and THEN abort it, that’s a whole other matter that I prefer to stay out of.
