The effects of maternal wildfire exposure: a 28-year longitudinal study of Chile wildfires and neonatal outcomes.

BACKGROUND

Wildfires are an increasingly important source of air pollution and environmental stress, yet their impacts on perinatal health in middle-income countries remain poorly understood. Chile has experienced a marked rise in wildfire activity over the last three decades, providing a unique setting to study these associations.

METHODS

We conducted a nationwide panel data analysis using a municipality-month panel for 1990-2017 by aggregating individual birth records to municipality-month cells and linking them to municipality-month wildfire indicators in the mother's municipality of residence. Exposure was measured using the number of wildfires, cumulative duration, and burned area. We estimated two-way fixed-effects panel regressions (municipality and year-month) for mean birth weight, newborn length, and gestational age, adjusting for maternal, infant, and contextual characteristics. Wildfire duration was scaled in 24-h increments, and burned area was expressed per hectare to facilitate clinical interpretation.

RESULTS

Wildfire exposure during pregnancy was associated with small but potentially meaningful reductions in fetal growth. Each additional 24 h of cumulative wildfire duration in the maternal municipality was associated with an average ≈8-gram lower birth weight (95% CI: -16.8 to 0.7 grams) and a 0.05-cm shorter birth length (95% CI: -0.11 to 0.01 cm). Each additional hectare burned was associated with a reduction of about 0.73 grams in birth weight (95% CI: -0.93 to -0.53) and 0.01 cm in length (95% CI: -0.02 to -0.00).

CONCLUSIONS

Prolonged and extensive wildfires during pregnancy are associated with modest reductions in birth weight and length, particularly when exposure occurs in late gestation. Although individual-level effect sizes are small, they may translate into clinically relevant shifts at the population level in settings experiencing increasingly frequent and severe wildfire seasons. Our findings underscore the importance of monitoring wildfire activity and protecting pregnant women from sustained smoke exposure as part of climate adaptation and perinatal health policies.