Exposure to Rising Temperature during pregnancy linked to Increased Severe Maternal Morbidity

The US is witnessing a concerning surge in severe maternal morbidity (SMM), and new research suggests that rising temperatures due to climate change might be contributing to this alarming trend. A recent retrospective population-based epidemiological cohort study published in the Journal of American Medical Association shed light on the potential link between maternal heat exposure and SMM.

The research identified three levels of heat exposure: moderate, high, and extreme heat days. These were defined by daily maximum temperatures exceeding specific percentiles during the May to September period from 2007 to 2018 in Southern California. Long-term exposure, measured by the proportion of different heat days during pregnancy and by trimester, revealed significant associations with SMM, particularly during the third trimester. High exposure to extreme heat days during pregnancy and the third trimester correlated with a concerning 27% and 28% increase in SMM risk, respectively.

Short-term exposure was represented by various heatwave definitions, all of which displayed elevated SMM risks. These risks ranged from 32% under the mildest definition (daily maximum temperature exceeding the 75th percentile for at least two days) to a staggering 139% under the most severe definition (daily maximum temperature exceeding the 95th percentile for at least four days).

Furthermore, the study uncovered that mothers with lower educational attainment or pregnancies beginning in the cold season (November through April) faced greater risks. These findings highlight the vulnerability of certain populations to the adverse effects of maternal heat exposure.

The implications of this study are significant, particularly in the context of a changing climate. As global temperatures continue to rise, the risk of extreme heat events during pregnancy becomes more pronounced. These extreme heat events can potentially lead to severe maternal morbidity, threatening the well-being of both mothers and infants. Improved access to cooling facilities during heatwaves, targeted support for at-risk populations, and enhanced education regarding heat-related risks during pregnancy, could play a pivotal role in reducing SMM cases. 

Source:

Jiao, A., Sun, Y., Avila, C., Chiu, V., Slezak, J., Sacks, D. A., Abatzoglou, J. T., Molitor, J., Chen, J.-C., Benmarhnia, T., Getahun, D., & Wu, J. (2023). Analysis of Heat Exposure During Pregnancy and Severe Maternal Morbidity. In JAMA Network Open (Vol. 6, Issue 9, p. e2332780). American Medical Association (AMA). https://doi.org/10.1001/jamanetworkopen.2023.32780