There's some interesting stuff written on this topic. Ethicists who tend in Kant's direction are very interested in the issue of the personhood of a fetus.
One general test that Kantian's apply is similar to the golden rule test; would you want the act done to yourself. Since most people (unless they are suicidal), when asked if they wish their mother had aborted them, answer in the negative, there is a prima facie case that abortion violates this basic rule. Aborted fetuses, if they had survived, would not have wanted to be aborted, hence they were treated as means to ends and not ends in themselves.
The problem arises when the issue is pushed back a little further. Fetuses not conceived, because the parents did not have intercourse would also have the same opinion of their own non-existence as aborted fetuses. They would have been treated as a means to an end.
So, at all times that a fertile adult is not engaging in sexual intercourse for the purpose of reproduction, they are treating their future offspring as means to ends and not ends in themselves. This would mean women should remain pregnant for all their fertile years.
Most people who oppose abortion are not happy with that conclusion.

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