Babies of South Asian and Chinese ancestry are smaller at birth than those of European ancestry, say B.C. researchers who suggest standardized growth charts aren't the best way to evaluate a newborn's health.

Dr. Patricia Janssen says some parents of small babies may suffer unnecessary anxiety over their newborn's progress.
(CBC)

In fact, some parents of small babies may suffer unnecessary anxiety over their newborn's progress, says University of British Columbia perinatal epidemiologist Patricia Janssen.
 
"The baby might be subject to particular tests such as blood tests that are invasive and uncomfortable just to see if there was any metabolic derangements that contributed to that small birth weight," Janssen told CBC News.

"In fact the baby might be completely healthy and not need any of that."

In the study, published in Wednesday's edition of the peer-reviewed journal Open Medicine, Janssen and her colleagues examined nearly 2,700 babies born at between 37 and 41 weeks gestation to healthy mothers. None of the mothers used tobacco, alcohol or drugs.

Nearly 1,200 babies were born to parents of European descent, 975 to parents of Chinese descent and 525 to South Asian parents.

The researchers found Chinese and South Asian babies were on average a little more than 225 grams smaller than babies of European ancestry. The average weight of a European baby born at 40 weeks was 3.66 kilograms.

They also found Chinese babies were "significantly" shorter than European babies — by 0.89 centimetres — and that South Asian babies were somewhere between the two. European babies born at 40 weeks were on average 50.5 centimetres.

Drawing on this research, Janssen has now created new fetal growth charts available to doctors across Canada.

Dr. Ajantha Jayabarathan, a family doctor in Halifax, says she's pleased to have access to the new information.

"It is extremely relevant to me that we actually look at sub-groupings of people in terms of how we define what is average," she told CBC News.

The B.C. researchers examined only Chinese, South Asian and European babies, but they say newborns of other ancestries may also differ in birth size from the norm.

They are at pains to point out that their study does not explain why these differences exist, or what the long-term consequences may be, calling for more research into these questions.