Impact of air pollution on low birth weight in Spain: An approach to a National Level Study

According to the WHO, low birth weight (<2500 gr) is a primary maternal health indicator as the cause of multiple morbi-mortality in the short and long-term. It is known that air pollution from road traffic (PM₁₀, NO₂) and O₃ have an important impact on low birth weight (LBW), but there are few studies of this topic in Spain. The objective of this study is to determine the possible exposure windows in the gestational period in which there is greater susceptibility to urban air pollution and to quantify the relative risks (RR) and population attributable risks (PAR) of low birth weight associated with pollutant concentrations in Spain.

We calculated the weekly average births with low birth weight (ICD-10: P07.0-P07.1) for each Spanish province for the period 2001-2009, using the average weekly concentrations of PM₁₀, NO₂ and O₃, measured in the capital cities of the provinces. The estimation of RR and PAR were carried out using generalized linear models with link Poisson, controlling for the trend, seasonality and auto-regressive character of the series and for the influence of temperature during periods of heat waves and/or cold. Finally, a meta-analysis was used to estimate the global RR and PAR based on the RR obtained for each of the provinces.

The RR for the whole of Spain is 1.104 (CI95%: 1.072, 1.138) for the association between LBW and PM₁₀, and 1.091 (CI95%: 1.059, 1.124) for the association between NO₂ and LBW. Our results suggest that 5% of low birth weight births in the case of PM₁₀ and 8% in the case of NO₂ could have been avoided with a reduction of 10 μg/m³ in the concentrations of these pollutants.

The impact of the results obtained- with 6105 cases attributable to PM₁₀ and up to 9385 cases attributable to NO₂ in a period of 9 study years- suggest the need to design structural and awareness public health measures to reduce air pollution in Spain.