Study identifies molecular changes associated with hotter weather and preterm birth

Emory University

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An Emory University study, published Friday by Science Advances, provides the first evidence that exposure to higher temperatures during pregnancy is linked to specific biological changes in mothers that are also associated with preterm birth.

A team of researchers from Emory University’s Rollins School of Public Health and School of Medicine conducted a novel molecular analysis of blood samples from 215 pregnant women living in metropolitan Atlanta, whose pregnancies ended in either full-term or pre-term live births (delivery before 37 weeks of pregnancy), and then matched the mothers’ residential addresses with the maximum ambient temperature experienced throughout their pregnancies.

This first-of-its-kind analysis found that several naturally occurring substances, such as methionine, proline, citrulline, and pipecolate, are disrupted when temperatures are higher. These amino acids and vitamins play key roles in managing stress and energy in the body, suggesting that heat-related biological strain may increase the risk of preterm delivery.

Previous scientific evidence suggested hotter weather impacted biological factors such as oxidative stress, heart and vascular issues, inflammation, and the premature rupture of membranes. However, this was the first study to pinpoint the potential molecules and pathways associated with heat and premature birth outcomes.

“As temperatures have increased, we’ve observed an increased association between more babies being born preterm after the weather was hotter, but scientists still don't know what exactly is happening in the body—and we really need to understand this to develop effective ways to protect mothers and babies,” says study lead author Donghai Liang, PhD, associate professor of environmental health at Rollins.

“We used the innovative metabolomic technology to specifically focus on the small molecules, or ‘molecular fingerprints’ as we call it, and learned for the first time that when the weather was hotter, the mothers’ blood shows some measurable changes in several important molecules and pathways that manage how the body deals with stress or makes energy. And these same kinds of changes were also seen in those mothers who gave birth prematurely.

Preterm birth is a leading cause of infant illness and death, but little is known about the biological reasons behind it, especially in relation to environmental stressors.

“By identifying these shared metabolic pathways between hotter temperatures and preterm births, this study could open the door to developing early biomarkers that could help identify pregnancies at higher risk and potentially inform prevention strategies or clinical interventions to support healthier pregnancies,” Liang says.

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Journal

Science Advances

DOI

10.1126/sciadv.adw8328 

Article Title

Critical windows of prenatal heat exposure and preterm birth: Metabolomic study in the Atlanta African American Maternal-Child Cohort

Article Publication Date

21-Nov-2025

 

Improving snowfall forecasts in the Mountain West

Utah atmospheric scientists use manually gathered snowfall data from across the West to train a new Model T

University of Utah

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image: 

Peter Veals measures snowfall using a coring tube and scale at a study plot in Utah.

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Credit: Peter Veals, University of Utah

The varied topography of the Western United States—a patchwork of valleys and mountains, basins and plateaus—results in minutely localized weather. Accordingly, snowfall forecasts for the mountain West often suffer from a lack of precision, with predictions provided as broad ranges of inch depths for a given day or storm cycle.

The crux of the problem lies in the snow-to-liquid ratio (SLR), which varies widely in the West.

“If you don't have a good snow-to-liquid ratio, your snowfall forecasts are not going to be as good,” said Peter Veals, a research assistant professor of atmospheric sciences.

New research by Veals and a group of University of Utah scientists aims to improve methods of forecasting by applying machine learning to manually collected snowfall data from 14 mountain sites by snow-safety professionals employed by ski areas and transportation departments.

It's all about snow density

The single most important predictor of SLR is the snow-water equivalent, or SWE, according to Veals.

 “It's because the more SWE you have, the more the storm’s snow weighs and it densifies itself. It compacts under its own weight,” said Veals, the study’s first author. Other factors including elevation, temperature, and wind speed also play a crucial role in determining what the SLR will be in each storm.

The U research team, led by atmospheric sciences professor Jim Steenburgh, has another study coming out soon applying this method across the continental United States, using snowfall data gathered at 900 locations.

The main reason why snowfall forecasting in the West is so much harder is that the amount of snow piling on the ground depends on not just on how much water the snow contains, but how dense or powdery the snow is, that is its snow-to-liquid ratio. SLRs can be as low as 2-to-1, or two inches of snow equaling an inch of liquid water, typical of slush. Or up to 100-to-1 seen in ultralight powder.

The commonly cited 10-to-1 “rule of thumb” for SLR was a product of Eastern weather forecasting.

“Somebody cooked that up in some place a long time ago. It's easy to use. It's just multiplying by 10,” Steenburgh said. And it has little relevance to the West.

To build a forecast model tailored to the West, Steenburgh and Veals’s team acquired manually gathered snowfall data from 14 mountain sites across the Western states, spots where avalanches are a winter hazard that must be managed with care.

Three sites were in Utah: Alta in Little Cottonwood Canyon; the Spruces campground in Big Cottonwood Canyon; and Aspen Grove in Provo Canyon. The others were in the Cascade and Sierra Nevada ranges, Colorado, Idaho, Wyoming and Montana.

The importance of manually collected snowfall data

Over the six-year study window, the team tapped a data source that was already being gathered regularly by experts tasked with keeping mountain corridors and recreation areas safe from avalanches.

“There's a bit of a mad scientist component to this,” Steenburgh said. “A lot of this work is what we call data wrangling. Just getting the data sets together.”

During every storm cycle, trained professionals made daily or twice-daily manual measurements, recording the height of the accumulated snow, its water content and time of day. Snow was measured by hand because automated gauges can’t always accurately record snowfall in windy conditions.

“No one's out there twice a day with a tube on a board, taking the core, weighing the snow, recording it, sweeping the board for the next day, recording the time they took the observation,” Veals said. “You have to be more meticulous than the average person to do this work. Ski patrols do that because they want to know how much snow is in their avalanche paths.”

The research team used this high-quality data to train new machine-learning models using an array of weather variables, including temperature, wind speed and specific humidity, to predict SLR with greater accuracy.

Their models, particularly the version created by a machine learning technique known as a “random forest,” greatly outperformed existing methods.

“There was one algorithm that was slightly more skillful, but it was 10 times the processing power, so that wasn't feasible,” Veals said. “You need to run this stuff on a huge data set every six hours and you need it to be done in two minutes.”

Yet the random forest model could explain nearly half of the variability in snow density compared to less than a quarter for current operational models. In simple terms, the new approach will enhance the reliability of snowfall forecasts, which would be helpful for the West’s water resource managers, highway officials, weather forecasters and avalanche professionals who depend on knowing how much water the snow holds.

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The study, titled “Predicting Snow-to-Liquid Ratio in the Mountains of the Western United States,” appears in the October edition of Weather and Forecasting published by the American Meteorological Society. Funding came from the National Oceanic and Atmospheric Administration (NOAA). Co-authors include scientists from the University of California, Berkeley; NOAA; Colorado State University; and the National Weather Service.

A weather monitoring station in Alta Ski Area, where snowfall data was recorded for the study, along with 13 other mountain sites around the West. 

Credit

Peter Veals, University of Utah

Peter Veals demostrates how a coring tube is use to gather and weigh snowfall.

Credit

Brian Maffly, University of Utah

Journal

Weather and Forecasting

DOI

10.1175/WAF-D-24-0233.1 

Method of Research

Computational simulation/modeling

Subject of Research

Not applicable

Article Title

Predicting Snow-to-Liquid Ratio in the Mountains of the Western United States

 

Sharper, straighter, stiffer, stronger: Male green hermit hummingbirds have bills evolved for fighting

University of Washington

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A female green hermit hummingbird hovers before a flower. 

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Credit: Jan Lenaert

Let’s get one thing out of the way: All hummingbirds fight. Most species fight for food, using their tiny bodies and sharp bills to force competitors away from flowers. But the green hermit hummingbird, which lives primarily in mountain forests of Central and South America, fights to win a mate.

“They gather together at a place in the forest that looks just like a singles bar,” said Alejandro Rico-Guevara, an associate professor of biology at the University of Washington. “They all have perches, and if someone else takes their perch — their place in the singles bar — they go bananas, and they fight.”

Hummingbirds’ weapon of choice? Their own bills. Like medieval knights in a joust, the birds raise a long, needle-thin bill into the air before driving it into their opponent. The stakes are high: Hummingbirds also use their bills to eat, poking them deep into flowers to reach nutrient-rich nectar. Losing a fight means a hummingbird might not find a mate. Breaking a bill could mean they starve. 

New research led by researchers at the UW Burke Museum of Natural History and Culture, where Rico-Guevara is the curator of birds, found that these fights have shaped the species’ evolution, yielding significant differences in bill shape for male and female green hermits. Compared to their female counterparts, male green hermits’ bills are straighter, sharper and structurally stronger. The straighter bills work better as weapons, while female birds’ more curved bills provide improved access to nectar in some flowers. The findings suggest that green hermits’ bill sexual dimorphism — when two sexes of a species exhibit different characteristics — was likely driven by their tendency to fight, not solely by ecological factors.

“Adult male green hermits have reinforced bills because they fight so much,” Rico-Guevara said. “It’s the same tool, but in very different contexts. This is an example of how much we can still learn from sexual dimorphism in nature.” 

In the study, published Nov. 10 in the Journal of Experimental Biology, researchers selected green hermit specimens from the Ornithology Collection at the Burke Museum and used photogrammetry to develop 3D models of male and female bills. Through curvature and angle analyses of those models, researchers found that male bills are 3% straighter and 69% sharper, respectively, with a dagger-like tip not found on female bills.

But the differences, researchers found, extend beyond bill shape. CT scans revealed that the male bill’s internal structure provided additional strength by transmitting forces more efficiently. 

Finally, researchers ran the models through a series of simulated stabbings to stress-test the bills in both head-on and angled attacks. They observed that the male’s straighter bill expends 52.4% less energy due to deformation, and is more resistant to breaking. The male bill experienced on average 39% less stress than the female bill. 

They also found that male bills’ straighter shape can accommodate a wider variety of attack angles, requiring less precision while fighting. 

“It’s a really cool example of sexually dimorphic weapons in birds,” said co-author Lucas Mansfield, a graduate student at Michigan State University who completed this work while studying at the UW. “When you think of sexually dimorphic weapons, you usually think of deer and moose, animals with big antlers. There aren’t many examples of things like that in the bird world. It’s fun to explore a more cryptic or hidden weapon.”

Co-authors include Felipe Garzón-Agudelo of the Centro de Investigación Colibrı́ Gorriazul in Colombia and Kevin Epperly, Ornithology Collections Manager at the UW Burke Museum. This research was funded by a Walt Halperin Endowed Professorship at the UW Department of Biology and by the Washington Research Foundation. 

For more information or to contact the researchers, email Alden Woods at acwoods@uw.edu. 

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Journal

Journal of Experimental Biology

DOI

10.1242/jeb.250769 

Article Title

Sharper, straighter, stiffer, stronger: sexually dimorphic bill shape enhances male stabbing performance in the green hermit hummingbird (Phaethornis guy)

Article Publication Date

20-Nov-2025