A study by researchers at Tulane University found that rising nighttime temperatures during pregnancy may be associated with an increased likelihood of autism spectrum disorder diagnoses in children. With global temperatures increasing, this study is the first to explore how heat exposure may impact fetal development.
“We need to think about exposure to heat around the clock,” Mostafijur Rahman, assistant professor of environmental health sciences at the Celia Scott Weatherhead School of Public Health and Tropical Medicine, said. “Heat waves are becoming more frequent, and people may only think of the dangers of daytime heat exposure.”
Researchers defined extreme heat as nighttime temperatures in the 90th to 99th percentile — roughly 3.6 to 5.6 degrees Fahrenheit hotter than average for a given area. Maximum daytime heat was not associated with an increased risk of ASD development.
While there was existing research on prenatal development and environmental factors linked to ASD, this study narrowed down the precise window of vulnerability during fetal development.
David Luglio, a postdoctoral fellow at the School of Public Health and Tropical Medicine, said the research team wanted to know if there are specific weeks when expectant mothers are more susceptible to high temperatures. That way, they can pinpoint which developmental events in the brain may be most affected by heat.
The research revealed that higher minimum night temperatures were associated with two sensitive time windows: weeks one through 10, which correlated with a 15% higher ASD development rate, and weeks three through 17, which were linked to a 13% higher rate.
Luglio said that some biological associations could explain the connection. For example, warmer nights may cause sleep disruption in expectant mothers, which could be a potential risk factor for ASD.
“One of the factors that we know is increasing is … temperature from climate change,” Luglio said. “It’s a logical place to look in terms of autism risk.”
A previous study that the team worked on in 2024 found that different pollution sources are associated with ASD development in children. Luglio said these results inspired the team to do more research on the effect of the environment on pregnancy.
A study released last year by the University of California, Los Angeles, the site of Luglio’s study, found that nighttime temperatures in California rise roughly three times faster than daytime temperatures. Since 2014, nine of the state’s 10 hottest temperatures on record have occurred during the night.