Summary: New research finds a notable association between unusually high nighttime temperatures during pregnancy and an increased risk of autism diagnosis in children.
A large retrospective study of nearly 295,000 mother–child pairs in Southern California found that exposure to hotter-than-usual nights during two critical periods of gestation — the first ten weeks and the final weeks of pregnancy — was linked to a measurable rise in autism risk. Specifically, exposure to extreme overnight heat in weeks 1–10 corresponded to about a 15% greater likelihood of an autism diagnosis, and exposure in weeks 30–37 corresponded to about a 13% greater likelihood.
The researchers observed the association only for nighttime (minimum) temperatures, not daytime maximum temperatures, suggesting that continuous 24-hour temperature exposure — and factors such as disrupted maternal sleep — may be important for fetal neurodevelopment.
Key Facts
- Critical developmental windows: The strongest links were observed during early pregnancy (weeks 1–10) and late pregnancy (weeks 30–37).
- Nighttime sensitivity: Associations were found for high overnight temperatures (Tmin) but not for daytime temperatures (Tmax), pointing to the importance of nighttime exposure and maternal sleep quality.
- Extreme heat thresholds: Increased risk was seen when nighttime temperatures exceeded the 90th percentile (approximately 3.6°F above average) and especially the 99th percentile (approximately 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.
Published in the journal Science of the Total Environment, the study analyzed nearly 295,000 births from Kaiser Permanente Southern California between 2001 and 2014. Investigators linked weekly outdoor temperature estimates at maternal residential addresses to autism diagnoses recorded in electronic health records by age five.
Comparing weekly minimum and maximum temperatures across gestation, the researchers found that extreme overnight heat during weeks 1–10 was associated with a 15% higher risk of autism and exposure during weeks 30–37 with a 13% higher risk. These comparisons reflect exposure at the 99th percentile versus the 50th percentile of nighttime temperature.
The study controlled for neighborhood characteristics, vegetation, and fine particulate air pollution, and the association for nighttime heat remained. The investigators noted they could not account for individual household factors such as access to air conditioning, which might modify exposure.
One possible explanation offered by the authors is that hotter nights are harder to avoid and may disrupt maternal sleep. Prior research has linked insufficient sleep during pregnancy with adverse neurodevelopmental outcomes, which provides a plausible pathway for how overnight heat might affect fetal brain development.
The research contributes to a growing literature on environmental influences on fetal neurodevelopment, including studies of air pollution and wildfire smoke. It also raises concern because nighttime temperatures have been rising faster than daytime temperatures in many regions; in California, nighttime warming has outpaced daytime warming by about threefold.
Lead author David Luglio, a post-doctoral fellow at Tulane’s Celia Scott Weatherhead School of Public Health and Tropical Medicine, emphasized identifying specific windows of vulnerability in pregnancy: “We identified particular gestational periods when exposure to higher nighttime temperatures was most strongly associated with autism risk,” he said, noting the potential for targeted preventive steps for expectant mothers.
Co-author Md Mostafijur Rahman, assistant professor of environmental health sciences, highlighted the broader public-health implications as heat waves become more frequent and nighttime heat increasingly common: “These results suggest the need to consider heat exposure around the clock, not only during daytime hours.”
Key Questions Answered:
A: The study authors propose both behavioral and biological reasons. Daytime heat can often be avoided by spending time in cooled indoor environments, but nighttime heat is harder to escape and can disrupt maternal sleep. Poor sleep and related physiological stress during pregnancy have been linked to adverse neurodevelopmental outcomes, so nighttime heat may pose a unique risk.
A: While the study did not have data on individual air-conditioning use, the findings point to the importance of a cool and comfortable sleeping environment during pregnancy. If nighttime heat contributes to risk through sleep disruption or heat-related physiological stress, maintaining cooler sleeping conditions could be a practical mitigation strategy.
A: This study is among the first to link prenatal nighttime heat exposure with autism risk. Nighttime temperatures are increasing faster than daytime temperatures in many regions, and these “tropical nights” may represent an environmental factor that warrants further investigation as climate warms.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context provided by 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. DOI: 10.1016/j.scitotenv.2026.181373
Abstract
Prenatal exposure to extreme heat and autism in children
Rising global temperatures have been linked to several adverse pregnancy outcomes, including neural tube defects and neurodevelopmental delays, but the relationship between gestational temperature exposure and autism has not been thoroughly examined. This retrospective cohort study evaluated weekly maximum (Tmax) and minimum (Tmin) temperatures during pregnancy and autism diagnoses by age five among births at Kaiser Permanente Southern California from 2001 to 2014.
Weekly Tmax and Tmin were estimated at mothers’ residential addresses using the gridMET model. The analysis used Cox proportional hazards models with nonlinear distributed lag structures to detect critical exposure windows. Among 294,937 children, 4,076 received an autism diagnosis by age five (approximately 80% male).
Extreme nighttime temperature exposure (Tmin) during gestational weeks 1–10 and 30–37 was associated with increased autism risk. Comparing the 99th to the 50th percentile of Tmin, the hazard ratio (HR) for weeks 1–10 was 1.154 (95% CI: 1.040–1.288) and for weeks 30–37 was 1.132 (95% CI: 1.030–1.246). No significant associations were observed for Tmax.
These findings suggest that exposure to high nighttime temperatures in specific prenatal windows is associated with a greater risk of autism diagnosis in children, underscoring the need for further research to clarify mechanisms and to evaluate potential public-health interventions as nighttime warming increases in a changing climate.