From this libertarian's pov, the right of the baby/fetus to live outweigh the mother's right to be free of the inconvenience of carrying it a few more months to delivery. On the other hand, I don't see how the baby/fetus can have a superiour right to life than the mother, in those extremely rare cases where continued pregnancy will definitely kill the mother.
No baby should die because it is termed to be invonvenient, and no mother should die for the sake of carrying a baby, come hell or high water, to a term which will prove terminal for one or both.