Environment/Climate Change
Extreme Heat and Preterm Birth Risk: Insights from Chilean Birth Data (1991-2020) Estela Blanco* Estela Blanco José Daniel Conejeros Álvaro González-Reyes Paola Rubilar Pablo Sarricolea
BACKGROUND: The relationship between extreme heat and preterm birth has been the focus of recent reviews and meta-analyses. Reports similarly conclude that exposure to high temperature during pregnancy may trigger a preterm birth. However, no studies addressing the relationship between extreme heat and preterm birth have been conducted in South America.
METHODS: We conducted a population-based cohort using information from birth records (1991-2020) and limited analysis to births in spring/summer (November to March; n= 969,842). Minimum and maximum daily temperatures were obtained from a gridded product CR2Met v2.5, that integrates re-analyzed data from ERA5, MODIS images, and in situ meteorological observations for the 33 urban municipalities of Santiago. Temperature percentiles and excess heat factor (EHF) were calculated for each municipality using historical data. EHF considers high historical temperatures (>95th percentile) and acclimatization in the previous 30 days. We calculated 15 metrics of heatwaves: 2, 3, and 4 consecutive days of temperatures >= 30 degrees Celsius, >=90th, 95th, and 99th percentile, and EHF for each municipality and assigned exposure (Yes or No) in the week and month prior to delivery. Cox proportional hazard models adjusted for maternal and paternal characteristics (age, education, occupation), newborn sex, vulnerability index for municipality, and year of last menstrual cycle.
RESULTS: Preterm birth occurred in 6% of births. There was spatial variability in extreme temperatures for the municipalities: 90th, 95th and 99th percentile ranged from 19 to 32, 20 to 33, and 21 to 34 ºC, respectively. Exposure to most heat wave metrics (2, 3, and 4 days at >=90th, 95th, and 99th percentile), did not relate to increased risk of preterm birth (Figure 1). Exposure to EHF for 2, 3, 4 days in the final week of pregnany was associated with 1.02 (95%CI 1.00-1.03), 1.02 (95%CI 1.00-1.04), and 1.03 (95%CI 1.01-1.05), respectively. Exposure to temperatures >= 30 degrees Celsius were associated with HRs <1 (Figure 1). Results were similar for exposure during the month prior to delivery.
CONCLUSIONS: We found evidence of increased risk of preterm birth, but only when evaluating exposure using EHF, a metric that considers acclimatization. Results from the Chilean population highlight the importance of evaluating and understanding regional impacts of climate change on child health.
