Pro-lifers have heavily criticized the notion of "abortion on demand" and have characterized women who have had abortions as using the procedure as a convenient form of contraception. Biting Beaver debunks that myth quite effectively in her post describing her own recent abortion:
I can firmly say that I do not believe that any woman uses the equivalent of a jackhammer to the guts followed by bleeding and clotting as well as no intercourse and 'light duty' for several weeks as birth control.
I think we can safely trust that women don't put themselves through this kind of thing without very good reason. Go read the whole post for a step-by-step account of what Biting Beaver's experience was like.
UPDATED: Of course, I should note that I do not presume to judge any woman's reason for having an abortion. Since I do not believe that abortion is the killing of a human being, I support "abortion on demand." If some woman wants to go through "a jackhammer to the guts" just because it's somehow more convenient than using contraception, that's her issue and I won't question her motives. Of course, it is often a question of poor or young women not having access to effective contraception, or education regarding same -- something that I wish both sides of the abortion debate would agree needs to be fixed.