I don't really want to get in an argument, so I won't reply beyond this, but here's a point I haven't seen around.

There's a lot of debate about when we can consider the fetus/baby a full human. Some people say even the single cell at conception is fully human, and some say that it doesn't become a separate human until the umbilical cord is severed. But the real answer is that we don't know. There's no bright line that we can definitely say "before this, it's just a part of the mother's body, after this, it's a new organism". All we can say is that some time between conception and birth (inclusive), it becomes human.

If that's the case, then at any point along the line, we have two possibilities for error: we could kill a human, or we could needlessly protect a non-human. Of the two, I consider the first to be rather the more egregious. Of course there are other factors, such as the fact that we are curtailing the mother's rights to protect the non-human, but still killing seems more extreme than a temporary restriction of rights.

By that reasoning, it would seem that the logical conclusion is to prevent abortion at any point after conception, but that's not necessarily the case. If we were able to assign weights to the gravity of each of the errors (say, killing a baby is twice as bad as restricting a mother's rights) and furthermore were able to assign a probability that the fetus is human at each stage of the pregnancy (naively, start at 0% at conception and increase linearly to 100% at birth), then there would be some point at which the chance at which it was human would match the weighted cost ratio, so that before that point abortion would be justified and after it we would prefer not to allow abortion.

Since no one that I'm aware of has done such an analysis, I'd prefer to err on the side of caution for now, so I am tentatively pro-life. I haven't actually had much opportunity to put that into practice, though, and I'm not really interested in seeking such opportunities out.