From what our breeder told us when we picked up Bella she was the runt of her litter but before long outgrew two of her siblings which were actually estimated to weigh under 4 lbs. She's 6.7 lbs now at 16 months (she just got weighed at the vet the other day when she got her shots) and very healthy. So being the runt of the littler does not mean they won't be healthy or will be too small. Bella was 3 months when we got her so it was obvious that she wouldn't be too small and she was very healthy. If the pup appears healthy and not too small or fragile I'd go for it.
Congratulations on your new baby!
