Sized for me. My bubs is nearly three weeks old and now weighs 7lb 3oz but the only nappies that fit him are XS BGs and small WNs. I've got small ittis, Teenyfits, small and mini BBs, small ecobubs, but they all have too much leg gape- he just wees out the sides! I've just bought loads more small BGs cos they are bombproof and actually fit him.
I've got loads of BTPs waiting for when he's bigger, but to be honest even these small nappies make his booty look huuuuge at the mo so i'll definitely not be putting him in btps for a good few months yet!! I haven't bothered buying many mediums though cos BTPs are better value for money.
eta: I think his smalls fit better when they're velcro- I prefer poppered nappies but the only ones I can get to fit nicely are aplix!