Embryonic matter...

Take the time to read The Unchosen Frozen: Second Thoughts on Biotechnology & In Vitro Fertilization, by William L. Saunders (March 2004 issue of Touchstone). Some excerpts:

The development of the embryo confirms its uniqueness as well as its humanity. Each human cell contains 46 chromosomes. Upon fertilization, the 23 chromosomes from the sperm are joined with 23 from the oocyte to produce the 46. The fertilized egg is now genetically complete and genetically distinct from its parents. With its unique set of 46 chromosomes, the fertilized egg is more than a simple cell like the sperm or the oocyte—it is a living human being. Beginning as a zygote (single cell), it develops into a morula (three days) and then into a blastocyst (five to seven days). In week two, it becomes a two-layer embryo, and in week three, a three-layer embryo. It continues to grow, through the eight-week embryo period and the subsequent fetal period, into a baby that a mother will one day hold in her arms. The human zygote produces specifically human proteins and enzymes. It genetically directs its own development. That growth is continuous, and, though the embryo undergoes significant change, it does not undergo what philosophers call substantial change—it does not change in nature from one kind of being into another. It possesses, from the first, the active capacity for full development... The desire of married couples for children is natural. Children are a fulfillment of the marital union. But no one has an absolute right to have a child. All life is a gift from God. He is not obligated to give it; we have no right to demand it. Thus, the natural desire of a married couple to have a child does not justify the use of any and all means that will produce a child... Perhaps because Americans were largely unwilling to face the realities of IVF and to wrestle with its moral implications when it first became possible, the country today stands on the brink of becoming a society in which moral reflection is reduced to a question of technical feasibility.