I'm surprised no one finds it odd that suigestu doesn't know whose dna he used and that both karin and sakura are in opposite locations and as a result not at the hideout to completely confirm sarada's mother. Kishi has created a set up by giving us an unknown dna object to use against sarada's own dna. If you are going by the manga and not by predictions/theories then its best to consider both sakura and karin as candidates for sarada's biological mother.
Right now all we truly know is that whatever dna was used, it matches with sarada's own dna.
The potential candidates for that dna is sasuke, sarada, karin (unlikely since karin village burned,she was captured and rescued by orochimaru) and maybe sakura (maybe but highly unlikely). Also, right now with the info we have and the picture we see it looks to be the umbilical cord. If it is the umbilical cord then more than likely sarada matched her own dna against her own dna. This doesn't change the fact that sarada's biological mother is either sakura or karin.