Maternal climate-related exposures and prolonged pregnancy: Findings from a statewide population-based cohort study in Western Australia

Unlike other pregnancy outcomes, climate-related exposures, and prolonged pregnancy (PP) (≥ 41 gestational weeks) have not been investigated. Space-time varying fine particulate matter air pollution (PM2.5) and the Universal Thermal Climate Index (UTCI) from three months of preconception through pregnancy were linked to 393,384 singleton births at ≥37 gestational weeks, including 12 % PP between 1st January 2000 and 31st December 2015 in Western Australia. Covariate-adjusted monthly-specific and cumulative odds of PP were estimated using distributed lag linear and non-linear logistic regressions. Every 1 μg/m3 PM2.5 and extreme UTCI exposures were associated with increased odds of PP with critical susceptible periods. Cumulative odds of PP for preconception up to the ninth pregnancy month were 1.06 (95 % CI 1.05, 1.07) per 1 μg/m3 PM2.5 increment, and 1.08 (95 % CI 1.02, 1.14) and 1.30 (95 % CI 1.23, 1.38) at 1st and 99th UTCI centiles relative to the median UTCI, respectively. Attributable burdens of high PM2.5 and UTCI exposures were 2085 (95 % CI - 4833, 10,234) and 853 (95 % CI 379, 1469) cases of PP, respectively. The identified vulnerable subgroups were mothers who were nulliparous, aged ≥35 years old, urban residents, complicated pregnancies, and male birth. This first epidemiological evidence suggests that climate-related exposures could contribute to prolonged pregnancy.