ubiquitin,
why only after head comes out do we say “ain dochin nefesh” why wasnt the fetus a nefesh before head coming out?
What changed?
The halacha does not state that the reason we can kill a fetus when the mother is endangered is because it is not a nefesh. Rather, it is a rodef. Once partial birth has commenced, perhaps we say ain dochin nefesh because the mother and infant are now both considered to be pursuing the other, and thus we cannot put more value on one than the other.