For a long time, I was pro life, because I don't believe there is any difference in the moral value of a baby immediately after it is born compared to before. Therefore, unless one believes that infanticide is moral, it would seem that one could not consider the abortion of a fetus immediately before birth as moral. Yes, their is probably a progression of the moral value of the fetus from the time of conception to the time immediately before delivery, but this becomes a fine line to draw.
Then I started to try to determine a moral equivalency to abortion that I could use to compare. I finally came up with what I believe is a pretty reasonable comparison, which actually changed my mind.
Consider a family with a child that needs a kidney in order to survive. Now imagine that the only person with a compatible kidney is the mother. Should it be legal to force the mother to donate the kidney? Thinking about this question, I felt, no, it shouldn't. I think it is morally reprehensible not to donate the kidney, but consider it even more so to force the mother to donate the kidney. Based on this, I also no longer believe that you can force the mother to deliver the child.
This also explains why I think abortions should be limited, however. I think abortions should be limited to the first trimester or 1 month after the mother first determines she is pregnant. Since I view the moral value of the fetus to be constantly increasing, approaching that of a baby over time, I think this decision needs to be made as early as possible. I compare this again to the kidney donation. If the mother signs a consent sheet saying she will donate a kidney, she can't keep changing her mind and switching back and forth. While it is her body, there are others affected by what she does with her body.
As for the generic, "It is her body, she can do what she wants with it" or "You can't tell a woman what to do with her body", these arguments are totally bogus. For example, we tell women everywhere that they can't use their body to beat their children. The real argument is that you can't tell a woman what to do with her body so long as her actions don't infringe on the rights of others. Now I realize a fetus has no well defined legal rights, I do believe the fetus has moral rights that should be considered, even if they currently aren't.