Ah, abortion. Quite the tricky topic.
On one hand, I can see where someone is coming from when they say a microscopic clump of cells, a blastocyst, isn't a person.
But on the other hand, it's quite obvious that a fully formed fetus, which PET scans show having neural activity, including dreams, is indeed a person.
So in my opinion, the upgrade from "life" to "personhood" happens somewhere in between those two stages.
Because it isn't just "killing" that makes abortion unlawful - it's the killing of a PERSON. We kill stuff all the time. And while animals do have rights (such as the right to not be subjected to types of suffering that don't occur in the wild, and the right to not be killed for fun), killing an animal is not quite the same thing as killing a person.
So what distinguishes a biological creature from a person?
Humans are, after all, animals. We are of the genus "homo sapiens." But we also have something EXTRA, in addition to animalhood - we have personhood.
A good possibility for where personhood starts would be the commencement of neural activity. If we can pinpoint the exact development stage where a fetus begins to have neural activity, then perhaps that's the beginning of personhood, and consequently, the point at which abortion transitions from "taking life" to "taking a person's life."
Or... perhaps... it's based on having a soul.
I've read that Tibetan Buddhists consider 49 days post-conception to be the point at which the soul enters the body. And on the other side of the world, the ancient Egyptians believed that the pineal gland is the organ through which the soul communicates with the body. And to bring it all together, modern science (Rick Strassman) notes that the pineal gland first appears in a developing fetus at... you guessed it... around 49 days post-conception.
Something to ponder.