Perhaps legally, but "medically and scientifically" is just you trying to impose your belief on the infant. Nobody has the right to commit murder.
in·fant (
n
f
nt)
n.
A child in the earliest period of life, especially before
he or she can walk.
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http://medical-dictionary.thefreedictionary.com/infant
fetus
[fē′təs]
Etymology: L, fruitful
the unborn offspring of any viviparous animal after it has
attained the particular form of the species; more specifically the human being
in utero after the embryonic period and the beginning of the development of the
major structural features, from the ninth week after fertilization until birth.
Kinds of fetal anomalies include
anideus,
lithopedion,
mummified fetus,
parasitic fetus, and
sirenomelia. Also spelled
foetus. Compare
embryo. See
also
prenatal development.
fetal, foetal, adj.
http://medical-dictionary.thefreedictionary.com/fetus
embryo /em·bryo/ (em´bre-o)
1. in animals, those derivatives of the zygote that
eventually become the offspring, during their period of most rapid growth, i.e.,
from the time the long axis appears until all major structures are
represented.
2. in humans, the developing organism from
fertilization to the end of the eighth week. Cf.
fetus.
3. in plants, the element of the seed that develops
into a new individual.em´bryonalembryon´ic
http://medical-dictionary.thefreedictionary.com/embryo