Honestly, I am dismayed that health professionals are trotting out this erroneous stuff about charts in the UK being for formula fed babies. As if!? So out of all the thousands of babies whose weight has been recorded to formulate the charts, the researchers have systematically selected only formula fed ones? Do they really think things work like that? The babies in the data sets were fed in all sorts of ways, which were not differentiated.
Littleducks, your very nice but very uninformed midwives etc need to use a bit of common sense, and also look at this which is an academic paper underlining the recommendations to use UK 90. UK 90 is the name of the charts issued in the UK in 1990 and used almost everywhere since about the mid-90s, replacing previous charts that were also based on thousands of babies, whose feeding was again undifferentiated.
I can't find anywhere that says 'these charts are based on formula fed babies' because no one sensible in the healthcare professions would even think that they were - the paper talks about 'healthy babies', I think, as being the 'candidates'.
Currently there are two lots of 'breastfed baby' charts floating around. One set is from the Child Growth Foundation, which is based on a very small number of babies in Cambridge - so it really is not enough of a mix or quantity to apply generally, and this is why it has not been adopted. The other set is from the World Health Organisation, and this is of a large sample of breastfed babies who were born at term and whose mothers were given bf support, and who fed more or less exclusively breast till 6 months. This is, unusually, a data set where the babies were differentiated, deliberately so.
So, UK 90 shows babies 'as they are' - it's a picture of the UK population. WHO charts show babies 'as they should be' - a picture of babies round the world fed according to the biological norm for our species.
Whichever you use, charts can only give you one small assessment of a baby's health. Individuals have their own individual needs and pattern.
And just to add: breastfed babies don't grow more slowly than formula fed babies, at least not at first. It's only after about 4-5 months that the WHO charts show bf babies falling away from the UK 90 chart.