The ambient temperature, especially heat, is increasingly recognized as a trigger for premature birth. A team from the Institute for Advanced Biosciences in Grenoble (CNRS, Inserm, Université Grenoble Alpes) delved deeper into this phenomenon. These research efforts, coordinated by Dr. Johanna Lepeule, a researcher at Inserm, shed light on an increased risk of prematurity linked to maternal exposure to heat (particularly at night) during early and mid-pregnancy. This discovery, published in the "International Journal of Epidemiology," holds particular significance in the era of climate change and rising temperatures.

Premature birth (delivery before 37 weeks of gestation) is currently the leading cause of mortality among children under 5 years old worldwide. Being born too early also increases the risk of adverse health effects throughout childhood and adulthood. Globally, approximately 11% of births are premature, and the rate is increasing in many countries. In France, for example, the rate of premature births has risen from 5.4% in 1995 to around 7% since 2016. While the drivers of these trends remain unclear, exposure to extreme temperatures is being pointed to as one of the contributing factors.

Today, we know from various scientific publications that high temperatures have an impact on health and are associated with mortality. But what about their impact on fetal development during pregnancy and the risk of premature birth? Most of the previous studies suggest an increased risk of prematurity associated with maternal exposure to ambient heat in the days leading up to delivery. The work carried out by Johanna Lepeule and her colleagues in the EDES team ("Environmental Epidemiology Applied to Development and Respiratory Health"), led by Rémy Slama and Valérie Siroux at the Institute for Advanced Biosciences, solidifies these signals and provides innovative results on this risk.

The researchers' goal was to assess the effects of heat and cold throughout pregnancy on the risk of premature birth. To do this, they precisely estimated weekly temperatures throughout pregnancy using advanced methods for 5,347 births from three mother-child cohorts: EDEN (Nancy and Poitiers), PELAGIE (Brittany), and SEPAGES (Grenoble). Temperature was examined from multiple angles: average temperature, nighttime and daytime temperatures, temperature variability, and heatwaves.

Periods of vulnerability to heat and cold during pregnancy.

Cold also emerged as a factor increasing this risk. The researchers discovered that exposure to low temperatures between the middle of the first trimester and the second trimester, as well as during the week before delivery, can increase the risk of premature birth.

« These results suggest that heat and cold could play an early role in pregnancy on the risk of prematurity. The next step in our research will be to understand the mechanisms, which are currently still unknown, » says Johanna Lepeule, a researcher at Inserm and coordinator of this research program.

"In the context of increasing temperatures and the frequency of extreme weather events that we are experiencing, the results of this publication should inform public health policies to reduce the burden of premature births," emphasizes Pierre Hainaut, Director of the IAB, University Professor, and Practicing Physician at CHU Grenoble Alpes.

Reference Article: Early delivery following chronic and acute ambient temperature exposure: a comprehensive survival approach Ian Hough, Matthieu Rolland, Ariane Guilbert, Emie Seyve, Barbara Heude, Rémy Slama, Sarah Lyon-Caen, Isabelle Pin, Cécile Chevrier, Itai Kloog, Johanna Lepeule

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