One of the big flaws with the thinking of a lot of pro-choice activists in their defense of legal abortions is they rely heavily on the notion that the thing being aborted is not a full fledged human being. While that is true and makes the position that abortions should be legal all the more sound it is far from critical.
Even if you grant the developing human full status as a human; equal to you or me; that still doesn't entitle it to use another person's body against that person's will.
One simple example is that no one is required to donate blood under any circumstances. And that is only a very minor inconvenience. Granted in the right circumstances people would think you're a miserable bastard for not donating but clearly no one has a right to your blood.
Another example is a follows. Let's say you wake up one day and find yourself attached to another person through a system of tubes. The people around tell you that the person you're attached to is a world class violinist and is suffering from liver trouble and needs to borrow yours for several months. This will limit your mobility and there is some fairly minor risks for you but now that the procedure has begun it cannot be stopped without killing the violinist. While it would be quite good of you to endure the procedure, you're rights were clearly violated. And again, the violinist has no right to use of your organs without your consent.
Some would argue that the crucial difference is that a pregnancy is the result of a willing action. But that logic doesn't work either. Many pro-life people will say that abortion is only acceptable if the mother's life is in danger, if the child would develop severe birth defects, or if the mother was raped. The problem with this position is that it says it's okay to murder an innocent child if the woman didn't want to have sex. But if the woman wanted to have sex then it's not okay. This turns the child into a punishment for wanting sex. And I think we can all agree that a child shouldn't be used as a form of punishment.