applied to a fetus too young to maintain independent life, by 1821, from French non-viable (by 1813 in the Code Napoléon); see non- + viable.
It is an established fact, that under the fifth month no foetus can be born alive--from the fifth to the seventh it may come into the world alive, but cannot maintain existence. The French term these non viable. We may designate them non-rearable, or more properly immature--in distinction to those between the seventh and the ninth month, which may be reared, and are termed premature. [John Gordon Smith, M.D., "The Principles of Forensic Medicine," London, 1821]