Just heard an interesting item on Radio 4 about the new WHO growth charts - basically explaining that these new charts are based on a number of babies brought up in ideal circumstances (according to the WHO) - eg non-smoking, exclusively breastfed until 4-6 months, breastfeeding continued into the second year.
Link to programme info
You can also look at the new charts here. I have a very large baby and was concerned that she would have been classed as overweight according to the WHO charts, although she was fully breastfed until 9 months. It is reassuring to see that they actually give a wider weight range rather than narrower, so my DD would have sat comfortably at the top of the range.