Likewise, age should not enter into the equation. We don't maintain that the old are worth more than the young. And who would seriously consider freezing their three year old child and placing them in suspended animation with a view toward thawing them at a future date?
Location outside the mother's womb shouldn't enter in to one's consideration about how to treat such embryos either. Location may affect the value of real estate, but it doesn't affect the value of human beings. We don't maintain that human beings who live in penthouse apartments have more inherent worth, value, or dignity than those who live in the ghetto.
"Embryo screening" is a practice by which parents are encouraged to "eliminate" embryos who might have undesirable genetic characteristics, such as the trait for early-onset Alzheimer's. Through a process called "pre-implantation genetic diagnosis" (PGD), embryos who are deemed at risk for carrying undesirable genetic traits are "weeded out." Aside from the fact that PGD poses a high risk that healthy embryos will be discarded, the practice embraces the notion that those who don't measure up to someone else's subjective standard of perfection do not have lives worthy of living. The immorality of such a practice for older children is manifestly apparent. We cannot justify the elimination of a two year old because it is discovered that they have a genetic trait that may cause problems for them in the future. The practice of weeding out two day old embryos is no more defensible.
"Selective reduction" is a course of action that is often recommended when more embryos than expected successfully implant in their mother's womb, e.g., five instead of two. Selective reduction is a euphemism for "abortion." Fertility experts often advise their clients to eliminate some of the babies they are carrying to avoid the stress of multiple births and to increase the likelihood that they will give birth to fewer, but healthier, children. Such a course puts the mother on the path of killing some of her children in utero to benefit the remaining ones. This "Sophie's Choice" recommendation clearly violates the ethical principles outlined above.
Couples who wish to avail themselves of reproductive technologies will do well to educate themselves about all that the technologies entail. They will do even better to evaluate those technologies in the light of ethical principles that should inform their decision making before embarking on their use.