Drinking diet soft drinks and other artificially sweetened beverages during pregnancy is associated with having overweight one-year-olds, according to a new report.

The researchers did not find a link between sugary beverages during pregnancy and babies’ body mass index (BMI), which is a measure of weight in relation to height.

Canadian researchers studied 3,003 mothers who delivered healthy babies between 2009 and 2012 and had completed diet questionnaires during their pregnancies. They then examined the babies when they were a year old. Almost 30 per cent of the women drank artificially sweetened beverages during pregnancy.

After controlling for maternal body mass index, age, breast-feeding duration, maternal smoking, maternal diabetes, timing of the introduction of solid foods and other factors, they found that compared with women who drank no diet beverages, those who drank, on average, one can of diet soft drink a day doubled the risk of having an overweight one-year-old.

The study, in JAMA Pediatrics, found no association with infant birth weight, suggesting that the effect is on postnatal, not foetal, growth. The mother’s consumption of sugar-sweetened drinks was not associated with increased risk for overweight babies.

“This is an association, and not a causal link,” said the lead author, Meghan Azad, an assistant professor at the University of Manitoba. “But it certainly raises the question of whether artificial sweeteners are harmless. It’s not time to ban them or tell everyone not to consume them, but there’s no great benefit to consuming these drinks, so there’s no harm in avoiding them.”

Although this study only included diet soft drinks and sweeteners in tea or coffee, these sweeteners can also be found in energy drinks and juices, said Mark Pereira of the University of Minnesota in Minneapolis, who co-authored an editorial alongside the new study.

Additional reporting from New York Times, Reuters.