Exposure to high temperatures can affect the growth of unborn babies during pregnancy and infants up to two years old, according to a new analysis.
A new analysis suggests that exposure to elevated temperatures can negatively influence the growth of fetuses during pregnancy as well as infants up to two years old.
This study is the first to demonstrate that heat stress can affect the development of babies after birth, expanding on earlier research that identified heat stress’s effects on fetal development.
The research analyzed data from infants and their mothers as part of a clinical trial in The Gambia, discovering a slight decrease in birth weight for each 1°C rise in daily average heat stress during the first trimester.
No growth effects were linked to heat stress experienced in the second trimester. While there was a tentative suggestion of an increase in head circumference relative to body size for those exposed to heat during the third trimester, this conclusion is less certain.
The study also found that infants up to the age of two who were exposed to high environmental heat may have lower weights and heights for their age. The most significant weight decreases were observed in infants aged 6-18 months who had high average daily heat stress in the preceding three months.
At 12 months, infants subjected to average heat stress equivalent to 30°C were more likely to be underweight for their height and age compared to those who experienced heat stress at 25°C.
These results were consistent for both male and female infants.
The research team, led by experts at the Medical Research Council Unit The Gambia (MRCG) and the London School of Hygiene & Tropical Medicine (LSHTM), emphasizes the urgent need for public health strategies that address the effects of heat exposure, particularly for pregnant women and their children, in light of climate change.
The findings have been published in The Lancet Planetary Health.
The data was collected during the Early Nutrition and Immunity Development (ENID) randomized controlled trial conducted in West Kiang, The Gambia, from January 2010 to February 2015. A total of 668 infants were monitored during their first 1000 days of life, which included 329 (49%) females and 339 (51%) males.
The trial analyzed how heat stress impacted fetal growth using recognized clinical measures of weight, length, and head circumference for gestational age, and likewise assessed the effect of heat stress on infant growth based on weight and height scores from birth to two years.
At birth, 66 (10%) infants weighed less than 2.5 kg, categorized as low birth weight, 218 (33%) were small for their gestational age, and nine (1%) were born prematurely.
Heat strain occurs when external factors, like weather or physical activity, disrupt the body’s ability to maintain its internal temperature. In this study, heat stress was quantified using the Universal Thermal Climate Index, which considers elements like heat, humidity, wind speed, and sunlight, assigning an equivalent temperature (°C) related to the risk of heat strain.
During the study, the average level of heat stress exposure was recorded at 29.6°C. The highest daily maximum was 45.7°C, while the highest daily minimum was 28.9°C.
Dr. Ana Bonell, Assistant Professor at MRCG and the study’s lead author, stated:
“Our study highlights that the combined crises of climate change, food insecurity, and undernutrition disproportionately impact the most vulnerable groups, including young children.
“These findings build on prior evidence that indicates the first trimester is particularly susceptible to heat exposure, making it crucial to investigate factors contributing to this relationship.
“It’s likely that heat stress affects appetite, food intake, and availability. We are also investigating potential direct influences on cellular and inflammatory pathways, which together may compromise the ability of pregnant women and infants to regulate their body temperature.”
“We need to identify which populations are most at risk for heat stress and where growth issues may be identified, to develop effective public health interventions.”
“With global rates of child malnutrition remaining alarmingly high and ongoing global warming, these findings should drive action to enhance child health.”
The researchers emphasize the need for further investigation into the relationship between heat stress and health outcomes in other regions besides The Gambia. The available data did not account for dietary habits, maternal infections, or socioeconomic factors, which may also affect fetal and infant growth.
The research received funding from Wellcome.
