As global temperatures rise, doctors have observed a troubling pattern: more babies are being born too early following periods of unusually hot weather.
A new study from Emory University adds important detail to that picture, pointing to subtle chemical shifts in the bloodstream that may help explain why.
The research, published in Science Advances, focuses on biological markers that have long been difficult to pinpoint.
While earlier work hinted that heat can affect inflammation, oxidative stress and cardiovascular strain in pregnancy, the precise mechanisms have remained largely unclear.
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Following heat exposure through the blood
To explore these hidden pathways, the team analyzed blood samples from 215 pregnant women in metropolitan Atlanta.
The participants experienced varying levels of heat exposure based on where they lived, allowing researchers to compare environmental conditions with molecular activity in the body.
Using metabolomic profiling, a technique that maps thousands of small molecules circulating in the blood, the scientists identified a set of amino acids that shifted noticeably during periods of higher temperatures.
Among them were methionine, proline, citrulline and pipecolate, compounds essential to managing stress responses and energy production.
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According to lead researcher Donghai Liang, these molecular changes resembled the patterns observed in mothers who later delivered prematurely, suggesting a shared biological route connecting heat exposure and elevated preterm birth risk.
Implications for maternal health in a warming world
Preterm birth remains one of the leading causes of infant illness and mortality, yet many of its root causes are still poorly understood.
The Emory findings offer a rare window into the early biological shifts that may increase vulnerability during pregnancy.
Researchers say the work could eventually support the development of early-warning biomarkers, signals in the blood that help clinicians identify pregnancies most at risk when temperatures rise.
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Although more studies are needed, especially across larger and more diverse populations, the results underscore the urgency of protecting maternal health as extreme heat becomes more common.
Sources: News Medical, and Science Advances.
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