A quarter of all British babies will be redefined as heavier than the norm, if new child growth charts produced by the World Health Organisation are adapted.
The Royal College of Paediatrics and Child Health is to decide next week if they back the adoption of the new WHO growth charts in the UK.
Babies' weights are now plotted against 1980s data based on how 30,000 grew.
The new WHO charts aim to show how breastfed babies "should grow", rather than how most babies do grow.
They are based on a select group of 8,000 babies from six cities around the world, who were entirely breastfed for six months, with continued breastfeeding into their second year, and where none of the families smoked.
The result of using this "ideal" sample of babies is a markedly changed growth curve for weight than the ones currently used in Britain - which include both formula and breastfed babies.
Breastfed babies put on more weight in the first few weeks but then slow down.
The 50th centile in the charts is the line showing a rate of growth where half will be above and half below.
The new 50th centile from the WHO shows growth after one year which is about half a kilo, or one pound lighter.
If the WHO charts are introduced, we will be comparing British children's growth to that of a select group representing the small faction of the population that meets the WHO criteria.
And it would mean that a quarter of all babies would, in one statistical sweep, jump from below the 50th centile to above it.
Tam Fry of the Child Growth Foundation said: "The medical profession will need to be educated to understand the purpose behind the charts so that parents who feed their babies formula do not worry that their babies are too heavy."
The Department of Health has adopted the WHO recommendation that mothers breastfeed babies for six months.
But currently only about 20% of mothers in the UK do so, and many of these also give their babies some formula.
The WHO argues that the new growth charts will help to promote breastfeeding as the optimal source of nutrition during infancy.
The Royal College of Paediatrics and Child Health College will produce a final recommendation to the Department of Health over whether the new WHO charts should be adopted by Autumn 2006.
Dr Patricia Hamilton, President of the RCPCH, said: "There are many practical implications that need to be carefully considered and any change should only occur after adequate notice."
BBC Radio 4's More or Less was broadcast on Thursday, 6 July, 2006 at 1500 BST. You can listen to the programme on Radio 4'sListen Again page.