On a philosophic ground I think there is a difference between something that's "life" and something that's "a person". Things like something's shape or having a heartbeat do nothing to solve that question. I don't worry about stepping on bacteria or grass because in a millions years it might evolve into a sentient species and would disrupt that. Since God, to my knowledge, hasn't come down and explained when that transition takes place in a human or even if it takes place at all before birth I think, from a legal standpoint, it should be erred on the side of the person that might have their own body forced to undergo something they don't want, like a pregnant women that wants an abortion, than for everybody else to play God and pretend they know they answer to that question, like opponents of abortions like to do, when they don't because nobody does.
On a personal level there is a lot I don't like about abortions, but I feel that if somebody wants to have an abortion I don't have a right to control that other person's body, and if there is an issue with that person and a higher being because of it that's something that person and the higher being will have to work out someday. It's not my business.
Having control of the medical issues that happen to ones body is a fundamental right of all people. In my opinion, somebody we know is a person exercising a fundamental right trumps what might happen to something that is only maybe a person but we don't if they are or not.