Hi baysmum,
the newborn nappies currently in the sale are a slightly larger size to other NB brands out there. I'm currently reviewing the sizing of the Newborn Nappies and the new cut will most likely be a little smaller. You can expect the nappies to fit your baby for at least 6-8+ weeks unless you have a very large Baby. My daughter was prem (5lb4oz) and fit her Newborn Nappies till she was 3 1/2 months. It kinda depends on the thighs and how quickly baby puts the chub on around them.