A recent study published in the Journal of the American Medical Association has uncovered a concerning association between pregnant individuals exposed to extreme heat and an increased likelihood of experiencing life-threatening complications during labor and delivery. This research, which highlights the impact of extreme heat on pregnancy, distinguishes between long-term exposure and acute events like heatwaves.
Ashley Ward, Director of the Heat Policy Innovation Hub at Duke University, who was not part of the study, emphasized the significance of this distinction. She stated, “Most of the research around pregnant women has centered on acute events like a heatwave… but honestly, what we are all experiencing this summer is an excellent example of really what I would consider chronic heat exposure.”
The study utilized data from Kaiser Permanente Southern California, a healthcare network, to identify more than 400,000 pregnancies in the region occurring between 2007 and 2018. Researchers then examined temperature data from the same period, utilizing daily maximum temperatures to determine the extent of heat exposure experienced by pregnant individuals during their pregnancies, broken down by trimester.
The study identified significant associations between both short- and long-term exposure (typically defined as 30 days or more) to environmental heat during pregnancy and severe maternal morbidity. Severe maternal morbidity, a term defined by the Centers for Disease Control and Prevention, encompasses 21 unexpected outcomes during labor or delivery that are considered near misses for maternal mortality. These outcomes include cardiac arrest, eclampsia, heart failure, sepsis, and ventilation. (The primary findings did not account for whether a blood transfusion occurred during delivery, as detailed data on this aspect were not available.)
Specifically, the research found that high exposure to extreme heat throughout the pregnancy or during the third trimester was associated with a 27 percent increase in the risk of these severe delivery complications. Exposure to a heatwave during the final week of pregnancy also correlated with an elevated risk of life-threatening delivery complications.
This summer witnessed record-breaking global temperatures, with cities such as Phoenix experiencing unprecedented heatwaves. While the study did not reveal significant demographic variations when examining data by race and ethnicity, it did highlight that individuals with lower education levels faced a higher risk of heat-related severe maternal morbidity. This finding suggests potential strategies for targeted interventions by healthcare professionals.
Anqi Jiao, an author of the study, explained, “They may pay more attention to these mothers with lower education levels as a targeted intervention. Those mothers with lower educational attainment may have very limited knowledge to understand extreme heat as an environmental hazard, and they may not understand why the extreme heat could affect their pregnancy outcome.”
Crucially, the study also established links between heat exposure and cardiovascular events during labor and pregnancy. Cardiovascular conditions have become a leading cause of pregnancy-related deaths in the United States, a crisis that has worsened in recent years despite medical advancements.
Ward commended the study’s focus on severe maternal morbidity, as it represents the most severe health outcome for pregnant women. Other studies have primarily explored the impact of heat on birth outcomes or maternal health conditions like gestational diabetes.
She suggested that future research could delve into overnight temperatures to uncover additional contributing factors to heat exposure, such as a lack of access to cooling during the night. Moreover, further investigations could illuminate the relationship between daytime heat exposure and various socio-economic factors, including the type of employment held by pregnant individuals.
Jiao indicated that her research team intends to explore different temperature metrics and climate factors like wildfire smoke in future studies.
Ward underscored the importance of this study for emergency planners, as it provides valuable insights into the dangers of chronic heat exposure. She stated, “These kinds of studies help inform those kinds of planning and preparedness activities so that they are targeted and that they have the most impact. Anytime we get research that helps us understand… the nuances of heat exposure, it helps us protect people better, and that information gets incorporated into the planning and preparedness infrastructure — at least that’s the hope, right?”
