Posted on January 30, 2022

Why Are Babies in Canada Getting Smaller?

Nicole Bogart, CTV News, January 19, 2022

An increase in the number of small-for-gestational-age births—an important indicator of infant health—has been observed in data that goes back more than 20 years in Canada.

And while the reasons for this increase remain largely unclear, a University of British Columbia (UBC) report hypothesizes that systemic issues such as immigration, economic stress and increasing maternal age may play a role.

Using Statistics Canada data that tracked trends in birth weight and small-for-gestational-age births, or SGAs, births among all single-baby live births in Canada from 2000 to 2016, the researchers found the mean birth weight for all births decreased from 3,442 grams in 2000 to 3,367 grams in 2016.

During the same time period, the rate of SGA births increased from 7.2 per cent in 2000 to eight per cent in 2016, corresponding with a 12 per cent increase in the odds of having a smaller baby in 2016 compared to 2000.

“Historically in Canada, we knew that babies were actually getting bigger, specifically between 1978 and 1996. That trend, at the time, was explained by sociodemographic factors and also by changes in maternal body size and maternal smoking,” study author Shiraz El Adam told by phone Wednesday.

“We used the same rationale and looked at population-level factors that have been changing over time in Canada that we know are also linked to a higher risk of a smaller baby.”

The study took into consideration sociodemographic factors previously associated with lower birth weight, including the birthplace of the baby’s mother and father.

In some countries, particularly in Asia, healthy babies are naturally smaller than they are in North America. With the increase in immigration rates in Canada, researchers hypothesized that immigration might explain the domestic decline in birth weight.

Results from the modelling showed that the odds of an SGA birth were indeed higher among births to parents born outside of Canada—but that only explained part of the decline.