UBC researchers looked at more than 100,000 babies born between 2006 and 2008 and found that those born to Chinese and South Asian parents were often wrongly classified.
Dr. Gillian Hanley said the problem is that baby weight charts are based on infants born to white parents only.
"It means when we were using the population-based distributions, which included a lot of white babies, which we know [are] bigger than Chinese and South Asian babies, what we were doing was misclassifying some small but healthy Chinese and South Asian babies as small for gestational age," she said.
The study says comparing babies within their own ethnic group could reduce health care costs, allowing resources to be targeted at newborns who actually need increased medical attention.
It could also reduce parental anxiety and unnecessary testing on healthy newborns.
Dietician Vanessa Lam says she meets many parents who are concerned that their baby is underweight.
"Parents always want to do a good job. The important thing to remember is weight is only one part, health is another good indicator," she said.
UBC researchers say further studies are needed, including research into the weights of babies of mixed ethnicity.