As YHWH says to the prophet Jeremiah, "Before I formed thee in the belly I knew thee; and before thou camest forth out of the womb I sanctified thee." From this passage, we can safely extrapolate that divine foreknowledge precedes conception, and that birth is a manifestation of a divine decision that is anterior to time.
In the case of an aborted fetus:
1) either God did not decree and foreknow that life, so aborting it was a manifestation of his mysterious will
2) or God did decree or foreknow but human action proved him wrong
If we entertain possibility 2) then we must also think that it's possible that other actions (wearing a condom, pulling out, or just plain neglecting to impregnate an egg) might also thwart God's knowledge and will. That is, every time a woman has a period, God might be really peeved, muttering to himself, "Medammit, I had named that one Pete! Turns out I was wrong! I HATE it when that happens!" So to avoid this divine embarrassment, we should not only outlaw abortion but also outlaw the failure to fertilize any and every human egg.
That seems implausible and also downright blasphemous, so we should stick to 1). In that case, abortion might be akin to any other manifestation of God's will that still leaves the human agent culpable (God is really, really annoying this way). Except there's a catch: in other cases (like murder, let's say), the sinful action that God has nonetheless foreseen (if not out and out decreed) manifests God's will in the real world. In the case of the aborted fetus, nothing is manifested in the world--it's as if God had actively willed nobody to be born and was then mad at us for not giving birth to anyone. That seems like the work of a bored God who entertains himself with acts of petulance.
There's only one way out of this dilemma. When God speaks to Jeremiah, he clearly draws a distinction between conception & fetal development ("formed thee in the belly"), on the one hand, and birth ("camest forth out of the womb") on the other. Divine foreknowledge happens with the former; election and sanctification happens before the latter. Clearly, this means that all fetuses are known by God as human life, but not all fetuses are sanctified. Abortion is an almighty God's judgment upon the world. Calling it wrong is blasphemy.