II’m sure you’ve seen them in your blue, red or purple book for your babies, the charts for tracking the weight, length and head circumference of your baby.

Simply put, if your baby is on the 50^th centile for weight this means that 50% of the population is heavier than him or her and 50% lighter. That’s ‘average’. If he or she is on the 90th centile only 10% of the population is heavier and 90% is lighter, and the same for height and head circumference.

Simple. But I keep meeting parents who worry about these charts:

• I met a baby recently […]