俱舍論記 18.45

18.45

「因彼血者至能長成」故者，答。因彼血渧以成身者，此是生母殺成逆罪，身生本故。第二女人但是養母，諸有所作應往來等事應諮後母，以彼後母能飲、能養、能長成故。故《正理》云「因彼血生者，識託方增故。第二女人但如養母，雖諸所作皆應諮決，而害但成無間同類。」

Regarding "The one due to whose blood [...] can bring to maturity": this is the answer. The one who constituted the body by relying on her drop of blood is the biological mother; killing her constitutes an anantarya offense because she is the origin of the body's birth. The second woman is merely an adoptive mother. All affairs concerning what should be done, comings and goings, and so on, should be consulted with the latter mother, because that latter mother was able to nurse, rear, and bring [the child] to maturity. Thus the *Nyāyānusāra* states: "For the one born due to her blood, consciousness lodged [there] and only then grew. The second woman is merely like an adoptive mother; although all actions should be deliberated and resolved with her, killing her only constitutes a peer of the anantarya."