Second, encouraging the donation of frozen embryos to prospective parents, even under the most optimistic scenario, would put only a small dent in the supply. According to a 2003 study, there are almost half a million frozen human embryos in storage in the United States. The vast majority of them -- 87% -- were frozen in case the parents might need them, but the vast majority of that vast majority will never be needed or used. An embryo-adoption drive wouldn't save the embryos that die in other stages of the process. And ironically, the recipients of donated fertilized eggs also generally have several implanted in the hope that one will survive. In effect, donation results in the deaths of embryos that would otherwise stay frozen.