Weight gain as a sign of pregnancy?

Hello! So backstory, I took in two chins from an older couple whose daughter had essentially dumped them on them. Male and a female whom we separated immediately. They said they’re daughter had been hoping for babies and the chins had been together for a year with “no luck” so I am hopeful that I didn’t get them right after they got pregnant, but know it’s a long possibility. I have the girl in a single unit critter nation because of the bar spacing, and have been handling her as little as possible for fear of hurting any potential kits. She looks fairly small to me, and I have been weighing her at the same time on the same day since she came in.

Week 1:
550g

Week 2:
556g

Week 3:
576g

My question is, is this continues weight gain a potential sign of pregnancy? How reliable of an indicator could it be? I’ve had some people tell me it could just be from the better food, etc. but thought I’d ask here as well. Regardless, we will continue the pregnancy watch for a full 120 days just in case.

Thank you in advance!