Here's a thought experiment. Put yourself behind a veil of ignorance. You don't know whether you will be put into a world in which abortion is prohibited, or not. You could pick a pro-life world, in which case you risk turning out to be the disadvantaged mother. You could pick a pro-choice world, in which case you could end up being the aborted fetus. Which do you pick?
I suppose if you think fetuses aren't persons, then there are no fetal positions in the original position, so this doesn't work on that assumption.