gavra_at_work and Sam2,
As gavra_at_work mentioned earlier, here is the Rambam in Hilchos Rotzeach u’Shmiras Nefesh (1:9):
?? ?? ???? ?? ???? ??? ???? ?? ??? ?????. ????? ???? ????? ??????? ???? ???? ???? ???? ????? ????? ??????. ??? ??? ??? ??? ???? ???? ????? ????? ??????. ??? ??????? ???? ??? ?????? ?? ???? ????? ??? ???? ??? ???? ???? ?? ????
1. The fact that the fetus can have the status of a rodef at all implies that it does have an aspect of personhood, if not perchance full status (e.g., in cases such as the halachos gavra_at_work quoted from Chovel u’Mazik, although perhaps it’s possible that the reason is that we’re not sure whether the baby will have been born viable at all?).
2. It would also seem to follow that if the fetus did not have the status of a rodef, it would be forbidden to kill it. I don’t think this point is disputed by any opinion.
3. As noted above in halacha 7, if it is possible to not kill the rodef to save the pursued, one should employ those means. Current medical technology makes this much more feasible than in previous centuries.