There’s this verse....
Psalm 51:5 Surely I was sinful at birth,
sinful from the time my mother conceived me.
Only human beings can sin. Here the Bible talks about sin from conception, not just birth. If there were no human, there would be no sin or sinful state.
The humanity of the fetus has been recognized in the past as well. There is the old English common law practice of *pleading the belly*. Although it applied to only cases where the woman was sufficiently along in her pregnancy for detectable movement to be felt, that was merely, no doubt, just a reflection of the available, or lack of available, technology to make any other more precise determination.
http://en.wikipedia.org/wiki/Pleading_the_belly
Here is the google search link to several other articles about the same concept.
The life of the flesh is in the blood and there is no blood flowing at conception and God was fully aware of that when He had it written.