The Overheating Womb: A Silent Risk to Brain Development
By Adhira Tippur and Sanjana Kavula
Summer 2023 was Houston’s hottest summer on record, with temperatures reaching 109°F. At Ben Taub Hospital, a physician noted an unusual uptick in pregnant women reporting fatigue, heat spells and dizziness. He recalled an uninsured patient in her second trimester, living without AC, who presented with an unexplained fever. As physicians rushed to cool her down, one question remained untested: what had the heat done to the baby’s developing brain?
In modern medicine, we know fevers during pivotal moments in pregnancy are linked to an increased risk of neural tube defects (NTDs) — serious birth defects where the brain, spine or spinal cord don't develop properly. However, the idea of studying heat’s effects on pregnancy isn't necessarily new, as women in the 1990s frequently used hot baths, saunas and heated spa treatments during pregnancy, unaware of the risks. According to a 1992 study published in JAMA, early pregnancy exposure to high temperatures significantly increased the risk of NTDs. The researchers of the study reported women who used hot tubs early in pregnancy had nearly three times the risk of having a child with an NTD.
The “90s Sauna Craze” and the correlation between fevers and NTDs highlight a critical finding: The developing fetal brain is sensitive to even the slightest temperature changes. And as heat waves intensify, exposing oneself to high temperatures during pregnancy is becoming an inescapable reality for many. Now, with more frequent heatwaves and unequal access to cooling resources, marginalized pregnant women may be unknowingly exposed to conditions that have high-risk thresholds. Yet, we are only beginning to understand how extreme heat may shape the fetal brain.
Understanding Heat’s Impact on Brain Development
Although growing evidence links heat exposure to developmental disruptions, significant gaps remain in our understanding of how temperature stress affects the fetal brain. Research shows heat can disrupt brain formation at multiple levels. At the molecular level, elevated temperatures impair ion channel function, disturb synaptic signaling and alter neural gene expression critical for development. Voltage-gated ion channels like vanilloid receptor subtype 1 (VR1) — which responds to noxious heat — can interfere with action potential generation and synaptic transmission during key periods. Dr. Fabrizio Gabbiani, a professor at Baylor College of Medicine, said, "even small temperature fluctuations can alter synaptic integration and response timing in neural circuits." In other words, even minor temperature changes can disrupt how brain cells communicate with each other and affect the precise timing needed for proper neural development.
Animal studies support these findings. Zebrafish, for example, which share over 70% genetic similarity with humans, show altered brain morphology and disrupted endocrine signaling when raised slightly above normal temperatures. Dr. Daniel Gorelick, an associate professor at Baylor College of Medicine, states zebrafish embryos raised slightly above their normal temperature exhibit altered brain morphology. A Quebec cohort study also found maternal exposure to 30°C during neural tube closure significantly increased risks of spina bifida and anencephaly. Most alarmingly, Dr. Richard Finnell, a professor at Baylor College of Medicine, found exposing pregnant mice to 43°C caused NTDs in nearly 80% of embryos.
Recent work by Dr. Bruna Corradetti, an assistant professor at Baylor College of Medicine, adds environmental stressors like heat and pollution can increase inflammation during pregnancy, disrupting fetal development. Using mouse models of NTDs, her team explores how stem cell-derived vesicles — tiny molecular packages with regenerative potential — may reduce damage by modulating the fetal environment.
Human studies confirm the brain’s sensitivity to temperature. Electroencephalogram (EEG) research shows heat stress reduces adult attention and memory, suggesting fetal brains under rapid development with weak temperature control may be even more vulnerable. Yet, broader neurodevelopmental outcomes such as cognitive function, remain underexplored in the context of pregnancy. There are, as Dr. Gorelick notes, "little known studies on pregnancy and heat's neurological effects." These research gaps leave clinical guidelines silent on heat exposure, meaning no screening, monitoring or intervention exists for affected pregnancies.
Real-World Implications
The neurological vulnerabilities documented in research take on urgent significance when viewed through an environmental justice lens. Cities like Houston, Phoenix and parts of Los Angeles are characterized as urban heat islands, or areas with significantly higher temperatures due to dense infrastructure and limited green space. Urban heat islands can exacerbate ambient heat levels by several degrees, and residents in these areas are predominantly low-income people of color, who live in housing without reliable air conditioning. Across the United States, 27% of households in the lowest income bracket lack access to any form of air conditioning. Consequently, during the record-breaking heat of summer 2023, opening a window or using a fan was the only option for many. Access to reliable cooling systems, prenatal care, stable housing and education about climate-related risks is not evenly distributed and often dictated by socioeconomic status. The womb, which was once considered one of the most protected environments, is shaped by the outside world.
Policy and Public Health
Solutions require coordinated action across research, clinical practice and policy. Dr. Finnell emphasizes the importance of early prenatal screening and believes temperature regulation should be part of obstetric screening protocols. Clinical guidelines should include heat exposure as a modifiable risk factor — like smoking or alcohol. Furthermore, policymakers should fund studies exploring how temperature extremes impact fetal neurological outcomes, particularly examining access to cooling resources among vulnerable populations.
Prenatal programs should consider offering temperature-control resources such as utility assistance or subsidized AC units to pregnant individuals during heat advisories. Hospitals could integrate heat exposure risk assessments into intake forms. At a higher level, federal agencies should recognize environmental heat as a neurodevelopmental risk factor, not just a cardiovascular one.
While few formal policies currently classify heat as a neurodevelopmental risk, federal initiatives such as the CDC's Heat & Health Tracker offer a foundation for future maternal heat-safety guidance. States like California have begun implementing Extreme Heat Action Plans that prioritize vulnerable populations, including pregnant individuals. Yet, none of these efforts directly address the neurological implications of prenatal heat exposure.
Conclusion
As global temperatures continue to rise, the story of the pregnant woman in her sweltering Houston apartment represents countless vulnerable mothers and their wombs exposed to extreme heat. While researchers document altered brain morphology in heat-exposed models and epidemiologists observe increased NTDs following maternal heat exposure, this knowledge remains absent from clinical protocols. The disproportionate impact on disadvantaged communities, where patients resort to wet towels and box fans in 100-degree apartments, adds an urgent dimension of environmental justice to this challenge. As temperatures climb, we must act, as there is a generation whose neurological development may be compromised by heat exposure in ways that demand immediate attention and intervention.