Premature births in Spain: Measuring the impact of air pollution using time series analyses

Premature birth (<37 weeks of gestation) is the principal indicator of neonatal death during the first month of life and the second cause of death of children under age five. There are 15 million premature births (PTB) worldwide. Air pollution in cities, primarily the result of urban traffic, greatly impacts PTBs, though there are few studies carried out on this topic at the country level. The objective of this study is to quantify the relative risks (RR) and the population attributable risk (PAR) of concentrations of contaminants on PTBs in Spain, and to analyze the most susceptible trimesters.

For each province average weekly PTBs were calculated (ICD-10: P07.2-P07.3) during the period 2001-2009 as well as weekly average concentrations of PM₁₀, NO₂ and O₃. Estimations were made of RR and PAR using generalized linear models with link Poisson, controlling for the trend, seasonality, the autoregressive nature of the series and the influence of temperature in periods of heat and/or cold waves. A meta-analysis was carried out to estimate RR and PAR at the global level based on the RR obtained for each of the provinces.

For all of Spain, the global RR of PTB due to the impact of PM₁₀ was 1.071 (1.049, 1.093) and 1.150 (1.084, 1.220) for NO₂, with no detected association for O₃. Therefore, with decreases of 10 μg/m³ in the concentrations of PM₁₀ and NO₂, around 12.5% and 4.5% of PTBs could have been avoided respectively.

Around 1.35% of PTBs that occurred in Spain during the study period can be attributed to air pollution. The adoption of structural measures to reduce these air pollutants should result in a decrease in the number of PTBs in Spain.