Researchers have found that women were more likely to have a son with autism if they consumed diet soda or other products containing the artificial sweetener aspartame while pregnant or breastfeeding.

The University of Texas Health Science Center at San Antonio scientists discovered that the mothers of boys who had been diagnosed with autism were three times more likely to say they drank at least one diet soda or consumed the equivalent amount of five tabletop packets of aspartame daily.

According to the New York Post, the researchers analyzed reported aspartame consumption of the mothers of 235 children with autism spectrum disorder. Then, they compared the results to a control group of 121 children who had “typical neurological development” and found that the male children with autism were more than three times more likely to have been exposed to aspartame-based products on a daily basis when they were in utero or breastfed. Interestingly, the researchers saw the association only in boys, but not for girls.

“Our study does not prove causality — it does not prove that maternal intake of diet sodas, and aspartame specifically, during pregnancy or nursing increases a child’s risk of autism — but it does raise a major warning flag,” said Sharon Parten Fowler, the lead author of the study. “Most of the autism cases in this study (87%) were male.”

No statistically significant association was found in female offspring according to a news release from UT Health San Antonio.

“Our findings contribute to the growing literature raising concerns about potential offspring harm from maternal diet beverage and aspartame consumption during pregnancy,” said Fowler, who has spent the past decade studying the health impacts of chronic exposure to non-nutritive sweeteners, including the risk of autism.

The researchers said that further studies including larger samples of both sexes are needed to evaluate these associations but warn that the possibility that early-life exposures to these foods through maternal diet might increase offspring neurodevelopmental risk, at least among boys.

“The findings suggest that women should exercise caution when considering use of these products during pregnancy and breastfeeding until further assessments are available,” said Fowler.