Heat, Humidity, and Adverse Birth Outcomes: Quantification of Projected Risks in the Contiguous United States
Research increasingly demonstrates relationships between higher apparent temperatures, inclusive of heat and humidity, and greater rates of preterm birth (PTB), term low birth weight (tLBW), and stillbirth cases. Through leveraging available epidemiological studies, we estimated the change in burden of these outcomes across the contiguous United States (CONUS) and throughout the 21st century during warm season months (i.e., May through September or October). We projected an additional 4,500 PTBs, 3,800 tLBWs, and 420 stillbirths annually at 1°C of CONUS warming attributable to changes in apparent temperature relative to baseline climatic conditions (1986–2005). These cases increased to 22,000 PTBs, 18,000 tLBWs, and 2,000 stillbirths annually with 4°C of warming relative to the baseline. We projected the most significant changes in per capita rates to occur in Gulf Coast states, where baseline risks of these birth outcomes currently are among the highest in CONUS. Across the three outcomes, we projected an increase in short-term healthcare costs following birth of approximately US$690 million annually at 1°C of warming, increasing to US$3.3 billion annually at 4°C (2023 dollars). When considering the economic burden of the infant deaths resulting from PTB and tLBW cases, we projected additional costs on the order of US$3.9 billion annually at 1°C, and US$35.8 billion annually at 4°C. Due to data availability, our valuation could not account for potential longer-term health and productivity implications or pain and suffering that families may experience following the adverse birth outcomes analyzed.