I actually think the personhood debate is irrelevant as well. The issue is mere property rights. Grant that the fetus is alive, grant that it is a person, you still have give an account for why a women owes it her body. The thing is rights generally incur a negative duty on others. That is if I have a right to A, then you have duty not to interfere with that right. You don't have a duty to take a positive act and enable my pursuit of A or to help me if someone else violates my right to A. You do not have a right to anothers body even if your ability to stay alive depends on it. A right to life does not constitute a right to be alive (without qualification). Judith Thomson laid some of this out in defense of her (what i think is too weak) position in her famous piece, "A Defense of Abortion". Here is the link and the relevant excerpt: http://spot.colorado.edu/~heathwoo/Phil160,Fall02/thomson.htm

1. Let us call the view that abortion is impermissible even to save the mother's life "the extreme view." I want to suggest first that it does not issue from the argument I mentioned earlier without the addition of some fairly powerful premises. Suppose a woman has become pregnant, and now learns that she has a cardiac condition such that she will die if she carries the baby to term. What may be done for her? The fetus, being to life, but as the mother is a person too, so has she a right to life. Presumably they have an equal right to life. How is it supposed to come out that an abortion may not be performed? If mother and child have an equal right to life, shouldn't we perhaps flip a coin? Or should we add to the mother's right to life her right to decide what happens in and to her body, which everybody seems to be ready to grant--the sum of her rights now outweighing the fetus's right to life?

The most familiar argument here is the following. We are told that performing the abortion would he directly killings the child, whereas doing nothing would not be killing the mother, but only letting her die. Moreover, in killing the child, one would be killing an innocent person, for the child has committed no crime, and is not aiming at his mother's death. And then there are a variety of ways in which this might be continued. (1) But as directly killing an innocent person is always and absolutely impermissible, an abortion may not be performed. Or, (2) as directly killing an innocent person is murder, and murder is always and absolutely impermissible, an abortion may not be performed. Or, (3) as one's duty to refrain from directly killing an innocent person is more stringent than one's duty to keep a person from dying, an abortion may not be performed. Or, (4) if one's only options are directly killing an innocent person or letting a person die, one must prefer letting the person die, and thus an abortion may not be performed.

Some people seem to have thought that these are not further premises which must be added if the conclusion is to be reached, but that they follow from the very fact that an innocent person has a right to life. But this seems to me to be a mistake, and perhaps the simplest way to show this is to bring out that while we must certainly grant that innocent persons have a right to life, the theses in (1) through (4) are all false. Take (2), for example. If directly killing an innocent person is murder, and thus is impermissible, then the mother's directly killing the innocent person inside her is murder, and thus is impermissible. But it cannot seriously be thought to be murder if the mother performs an abortion on herself to save her life. It cannot seriously be said that she must refrain, that she must sit passively by and wait for her death. Let us look again at the case of you and the violinist There you are, in bed with the violinist, and the director of the hospital says to you, "It's all most distressing, and I deeply sympathize, but you see this is putting an additional strain on your kidneys, and you'll be dead within the month. But you have to stay where you are all the same. because unplugging you would be directly killing an innocent violinist, and that's murder, and that's impermissible." If anything in the world is true, it is that you do not commit murder, you do not do what is impermissible, if you reach around to your back and unplug yourself from that violinist to save your life.

The main focus of attention in writings on abortion has been on what a third party may or may not do in answer to a request from a woman for an abortion. This is in a way understandable. Things being as they are, there isn't much a woman can safely do to abort herself. So the question asked is what a third party may do, and what the mother may do, if it is mentioned at all, if deduced, almost as an afterthought, from what it is concluded that third parties may do. But it seems to me that to treat the matter in this way is to refuse to grant to the mother that very status of person which is so firmly insisted on for the fetus. For we cannot simply read off what a person may do from what a third party may do. Suppose you filed yourself trapped in a tiny house with a growing child. I mean a very tiny house, and a rapidly growing child--you are already up against the wall of the house and in a few minutes you'll be crushed to death. The child on the other hand won't be crushed to death; if nothing is done to stop him from growing he'll be hurt, but in the end he'll simply burst open the house and walk out a free man. Now I could well understand it if a bystander were to say. "There's nothing we can do for you. We cannot choose between your life and his, we cannot be the ones to decide who is to live, we cannot intervene." But it cannot be concluded that you too can do nothing, that you cannot attack it to save your life. However innocent the child may be, you do not have to wait passively while it crushes you to death Perhaps a pregnant woman is vaguely felt to have the status of house, to which we don't allow the right of self-defense. But if the woman houses the child, it should be remembered that she is a person who houses it.

I should perhaps stop to say explicitly that I am not claiming that people have a right to do anything whatever to save their lives. I think, rather, that there are drastic limits to the right of self-defense. If someone threatens you with death unless you torture someone else to death, I think you have not the right, even to save your life, to do so. But the case under consideration here is very different. In our case there are only two people involved, one whose life is threatened, and one who threatens it. Both are innocent: the one who is threatened is not threatened because of any fault, the one who threatens does not threaten because of any fault. For this reason we may feel that we bystanders cannot interfere. But the person threatened can.

In sum, a woman surely can defend her life against the threat to it posed by the unborn child, even if doing so involves its death. And this shows not merely that the theses in (1) through (4) are false; it shows also that the extreme view of abortion is false, and so we need not canvass any other possible ways of arriving at it from the argument I mentioned at the outset.