Birth weight is important. Studies show that babies with higher than average birth weights are at an increased risk for obesity, heart disease, and even cancer. Lower than average birth rate, on the other hand, is no better and is recognized as one of the leading causes of neonatal mortality. Considering these risks, it’s important to determine exactly what the “average” birth weight is, and according to a recent Canadian study, it differs by ethnicity.

Doctors in Canada have noticed that although about one-third of births were from non-white immigrant mothers, the scale to weigh these newborns was still based on sizes of babies born from mothers with a Western European background. Due to this, many babies born to immigrant mothers, especially those from South and East Asia, may have been incorrectly labeled too small or too large for their gestational age, according to a recent press release.

Mislabeling a child as either under or overweight at birth can come with a number of health and financial consequences. For example, this may trigger unnecessary medical intervention, such as heightened monitoring and follow-up care. According to Dr. Marcelo Urquia, lead researcher of the study, failing to classify an at-risk baby is equally dangerous and can prevent some infants from receiving nessesary care. More importantly, the doctors noticed, that these weight discrepancies were largely based on race.

“World region-specific curves seem more appropriate than a single Canadian curve for assessing the impact of small [size] for gestational age and large for gestational age on adverse neonatal and obstetrical outcomes among some immigrant groups,” Urquia said in the press release.

Urquia and his team looked at 1,089,647 single births in Ontario between 2002 and 2012. Of these births, about one-third were of babies born to immigrant mothers, over half of which were of East and South Asian origin. In doing this, the team was able to develop a series of birth weight curves for specific regions of the world.

Results showed that newborns of immigrant mothers who were classified as small based on the Western European scaled chart were less likely to have lengthy hospital stays and/or die than newborns who were classified as small on the new adapted chart. This suggests that past classification methods had not been as accurate in their prediction of health risks.

One of the most notable opponents of the universal birth weight standards is the Swedish scholar Gösta Rooth. In 1980, he published his study, Low Birth Rate Revised, where he notably questioned the standard cutoff for low birth weight, arguing it does not account for variation in mean birth weights across countries. For example, an entry published in Princeton University’s Future of Children journal also found mothers of African origins tended to give birth to children of lower weights when compared to mothers of other ethnicities.

In the end, the researchers found that around five percent of babies born to immigrant mothers were deemed large for gestational age when using both curves, and 4.3 percent were classified as large when using only the world-region specific curve.

"Estimating the number of newborns conceivably spared unnecessary prolonged stay in hospital, special care, or referral for specialized pediatric or nutritional interventions, and the cost savings therein, is a worthwhile step in evaluating the impact of adopting world region-specific curves among certain immigrant populations," Urquia said.

Source: Urquia M, et al. Canadian Medical Association Journal. 2014.