Summary: New research has identified a significant link between extreme nighttime temperatures during pregnancy and an increased risk of autism in children.
By analyzing nearly 295,000 mother-child pairs, scientists discovered that exposure to unusually hot nights during critical windows of fetal development—specifically the first ten weeks and the final weeks of pregnancy—correlates with a 13% to 15% higher likelihood of an autism diagnosis.
While daytime heat showed no such association, the rising frequency of hot nights appears to be a major environmental factor, potentially disrupting maternal sleep and impacting the delicate process of prenatal neurodevelopment.
Key Facts
- Critical Developmental Windows: The highest risk was associated with heat exposure during the first trimester (weeks 1–10) and late in the third trimester (weeks 30–37).
- Nighttime Sensitivity: The study specifically found an association with nighttime heat but not daytime heat, suggesting that 24-hour monitoring of environmental exposure is essential for maternal health.
- Extreme Heat Thresholds: Risk increased significantly when overnight temperatures exceeded the 90th percentile (approx. 3.6°F above average) or the 99th percentile (approx. 5.6°F above average).
Source: Tulane University
Higher nighttime temperatures during pregnancy may be associated with a higher risk of autism diagnosis in children, according to a new study led by researchers at Tulane University.
The study, published in Science of the Total Environment, examined nearly 295,000 mother-child pairs in Southern California from 2001-2014 and found that warmer overnight temperatures were linked to increased autism risk during two key periods of pregnancy: early pregnancy and late pregnancy.
Children of mothers exposed to higher than typical nighttime temperatures during weeks 1-10 of pregnancy had a 15% higher risk of being diagnosed with autism. Exposure during weeks 30-37 was associated with a 13% higher risk.
Extreme temperatures that saw an increased associated risk of autism diagnoses among children were classified as above the 90th percentile (3.6°F hotter than the average) and 99th percentile (5.6°F higher than average).
These relative increases resulted in what researchers called a ‘significant’ association between hotter-than-average nights experienced by pregnant women and autism diagnoses for their children.
The findings add to a growing body of research exploring how environmental factors — including air pollution and wildfire smoke — may influence fetal neurodevelopment. As global temperatures rise, this study is the first to examine how temperature can impact that development.
On average, nighttime temperatures have risen three times faster than daytime temperatures in California, the site of the study, according to California’s Office of Environmental Health Hazard Association. And heat continues to be something for California residents to monitor, with nine of the state’s 10 hottest years on record occurring since 2014.
“Heat waves are becoming more frequent, and people may only think of the dangers of daytime heat exposure,” said Mostafijur Rahman, assistant professor of environmental health sciences at the Celia Scott Weatherhead School of Public Health and Tropical Medicine at Tulane University.
“These results indicate a strong association between high nighttime temperatures during pregnancy and autism risk in children and show that we need to think about exposure to heat around the clock.”
The study compared weekly outdoor temperature estimates at residential addresses with autism outcomes in children.
The association held even after the researchers accounted for factors such as neighborhood conditions, vegetation and fine-particle air pollution. The study was unable to account for other factors such as access to air conditioning.
Researchers did not find the same association with daytime temperatures, potentially due to people spending more time away from home during the day, making it more difficult to measure actual heat exposure.
“A key takeaway is that we identified specific windows when a mother and her developing child can be most affected by exposures to higher nighttime temperatures,” said lead author David Luglio, a post-doctoral fellow with the Celia Scott Weatherhead School of Public Health and Tropical Medicine.
“This is critical and hopefully can help mothers prepare accordingly.”
The study did not examine how higher temperatures at night could impact prenatal neurodevelopment. Luglio said it’s possible that higher temperatures at night can disrupt sleep for pregnant mothers.
A previous study found that too little sleep for pregnant women can be linked with higher risk of their children experiencing neurocognitive delays.
“Extreme heat exposure during pregnancy has been linked to a range of adverse health outcomes, including prenatal neurodevelopment delays and complications with an embryo’s development of a central nervous system,” Luglio said.
“The goal of our study was to specifically explore the link between prenatal heat exposure and autism diagnoses for the first time.”
The study was conducted in collaboration with Kaiser Permanente Southern California, University of Southern California, Harvard University, the Icahn School of Medicine at Mount Sinai, and Sonoma Technology, Inc.
Key Questions Answered:
A: Researchers suspect the difference lies in behavior and biology. People often seek air-conditioned environments or leave home during the day, but nighttime heat is harder to escape and directly disrupts maternal sleep. Poor sleep during pregnancy has already been linked to neurocognitive delays in children, suggesting a potential biological pathway.
A: While the study couldn’t account for individual AC usage, it highlights that controlling the sleeping environment is vital. If nighttime heat is indeed disrupting neurodevelopment via sleep loss or physiological stress, maintaining a cool bedroom during pregnancy could become a standard health recommendation.
A: Nighttime temperatures are rising three times faster than daytime temperatures in many regions. This study is the first to suggest that as our climate warms, these “tropical nights” may be an overlooked environmental factor influencing the increasing rates of autism diagnoses worldwide.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this autism and neurodevelopment research news
Author: Andrew Yawn
Source: Tulane University
Contact: Andrew Yawn – Tulane University
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Prenatal exposure to extreme heat and autism in children” by David G. Luglio, Xin Yu, Jane C. Lin, Ting Chow, Mayra P. Martinez, Zhanghua Chen, Sandrah P. Eckel, Joel Schwartz, Frederick W. Lurmann, Nathan Pavlovic, Rob McConnell, Anny H. Xiang, and Md Mostafijur Rahman. Science of The Total Environment
DOI:10.1016/j.scitotenv.2026.181373
Abstract
Prenatal exposure to extreme heat and autism in children
Increasing global temperatures have been associated with neural tube defects and neurodevelopmental delays. Effects of gestational temperature exposures on autism, another neurodevelopmental outcome with prenatal risk factors, have not been previously investigated.
This study examined associations of weekly maximum and minimum temperature (Tmax and Tmin, representing daytime and nighttime temperatures respectively) on development of autism in children in a retrospective birth cohort study from Kaiser Permanente Southern California hospitals from 2001 to 2014.
Autism diagnosis by age 5 was identified in electronic medical records with corresponding ICD codes. Weekly average Tmax and Tmin were estimated at the maternal residential addresses during pregnancy using the gridMET model.
Cox proportional hazard models with nonlinear distributed lags were used to identify critical windows of exposure with hazard ratios (HR) comparing exposure to temperature at the 90th and 99th percentiles versus the 50th percentile. A total of 4076 children (80% male) in the cohort of 294,937 had autism diagnosis by age 5.
Exposure to extreme Tmin during gestational weeks 1–10 and 30–37 were associated with increased risk of autism, with HR (95% CI) 1.154 (1.040, 1.288) for exposure during weeks 1–10, and 1.132 (1.030, 1.246) for weeks 30–37 comparing the 99th percentile to the 50th percentile. No association was observed for Tmax.
Exposures to high nighttime temperature during early and late pregnancy were associated with autism risk in children, a result of concern in a warming world.
Further research is needed to understand why daytime temperature was not associated with autism risk.
