Short term effect of air pollution, noise and heat waves on preterm births in Madrid (Spain)
Introduction
Preterm birth (PTB) refers to delivery before 37 weeks of gestation (Nguyen, 2005) and its prevalence ranges from 5 to 13% and represents the leading cause of perinatal mortality and morbidity in developed countries (Curran, 2014). In the last report Euro-PERISTAT, the PTB is still presenting a growing trend in Europe (European Health Perinatal Report, 2014).Preterm delivery can lead to serious infant health outcomes, including neonatal mortality and lifelong disability that range from pulmonary and circulatory to neurologic outcomes (Martin et al., 2000, Osmond and Barker, 2000). The etiology of PTB remains uncertain, but epidemiologic studies have consistently shown elevated risks with different environmental variables from ambient temperature (Schifano et al., 2013) to a number of measures of traffic-related air pollution (TRAP), including distance of residence from traffic corridors (Dadvand et al., 2014), exhausts components: mainly PM2.5 and NO2 (Iñiguez et al., 2015) or even traffic noise (Gehring et al. 2004).
In literature, land-use regression for estimating environmental variables and cohort design studies for estimating adverse birth outcomes are common methods. Most of these studies report a chronic effect during the entire pregnancy period (Kloog et al., 2015) or during different gestational windows (Bobak, 2000). Although recent birth cohort papers examine within-city variations both for air and noise pollution with highly resolved individual estimates at the scale of trimesters (Gehring et al., 2004; Dadvand et al., 2014). To date, few studies have looked at the effect of environmental variables on preterm delivery using a time series analysis (Sagiv et al., 2005). However, when using time series methodology removes the influence of covariates that vary across individuals but not within individuals over short periods of time.
Although, it is not clear the biological mechanism by which traffic related air pollution and noise or ambient temperature increases the impact on preterm births, there are epidemiological evidences that relate them to the short-term (Carolan-Olah and Frankowska, 2014). A growing number of previous studies have explored the association between air pollutants and preterm births, the most consistent findings reported were for positive associations with PM2.5, PM10 and NO2 (Guxens et al., 2014, Rappazzo et al., 2014, Pereira et al., 2014). About the underlying pathophysiological mechanism, PM2.5 and ultrafine particles seem to be which contribute most, related to a joint action between oxidative stress and pro-inflammatory state. Oxidative stress can be triggered by direct formation of reactive oxygen species when contacted with existing free radicals in blood, with soluble transition metal carrying by PM2.5 (Burton and Yung, 2011) or because organic materials such as PAHs (which may also be transported by PM2.5) have a high oxidative capacity themselves and can enter the cell and act in mitochondria (Li et al., 2003). Pregnancy physiologically originates a systemic inflammatory response in the mother. This inflammatory response is enhanced by the previously mentioned processes, leading to the possible occurrence of preeclampsia and other processes associated with premature birth (Redman et al., 1999).
Regarding noise levels little is known about the association between traffic noise and pregnancy outcomes. The available evidence on the impact of noise exposure on adverse birth outcomes is based primarily on exposure to occupational or aircraft noise (Figà-Talamanca, 2006). Exposure to noise may result in increased stress. Stress has been hypothesized to affect fetal growth through the endocrine system (Dancause et al., 2011). Moreover, there is evidence for an increased risk of hypertension in subjects exposed to noise which could increase the risk of adverse pregnancy outcomes. (Gehring et al., 2014).
About temperature's effect on adverse birth outcomes, there are few studies that reported positive associations, a recently published paper (Kloog et al., 2015) in which using space-time satellite data to determine air temperature (Ta) concludes that “Ta during pregnancy was associated with lower birth weight and shorter gestational age”. The results obtained pointed to associations between Ta and birth weight during the last trimester and Ta and preterm delivery and low birth weight during the entire pregnancy. These results are in accordance with those obtained by Dadvand et al. (Dadvand et al., 2014) whereby Ta has a stressful role influencing low birth weight.
Due to widespread of the exposure and the possible long-term health effects of PTB, exists a clear need to assess deeply the causes of preterm delivery that might be modifiable. The novel objective of this manuscript is to consider the environmental factors as acute short-term (from 0 to 7 days preceding birth) stressors that could provoke not only a higher number of deliveries, but also preterm births (deliveries before 37 weeks of gestation). To reach this aim we used time series methodology to analyze the short-term effect of air pollutants, noise levels and ambient temperature on the number of births and preterm births occurred in Madrid City during the period 2001–2009.
Section snippets
Study population
The city of Madrid is a densely populated metropolitan area situated in the central region of Spain. In the study period 2001–2009, it had a mean population of 3,164,245. The birth rate per 1000 population is 10.5 in Madrid city slightly higher to the Spanish rate: 9.1 (INE, 2013). The study population consisted of all live singleton births whose mothers resided in Madrid City and for whom birth certificates were filed between 1 January of 2001 and 31 December 2009. A total of 298,705 births
Study location
About air pollution and noise levels, this study is placed in the city of Madrid, with substantial levels of essentially TRAP and noise. Air quality in the capital still does not reach pollution limits set by the EU legislation for particulate matter with an aerodynamic diameter less 2.5 µm (PM2.5), as well as those recommended by the World Health Organization (WHO) for certain pollutants values (WHO, 2005). However for nitrogen dioxide (NO2) and tropospheric ozone (O3) concentrations the data
Exposure assessment and study design
A time-series analysis was performed to assess the short term impact of the following environmental variables; it was based on spatially aggregated data:
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Daily mean concentrations (µg/m3) of chemical air pollutants, Particulate matter less than 2.5 and 10 µm in diameter (PM2.5 and PM10), tropospheric ozone (O3) and nitrogen dioxide (NO2), were supplied by the Madrid Municipal Air Quality Monitoring Grid (http://www.mambiente.munimadrid.es/). This network consists of 27 urban background stations
Statistical analysis
We chose to fit autoregressive over-dispersed Poisson regression models due to the nature of the neonatal outcomes variables, daily counts of total births and daily counts of preterm births. Trends and seasonality were controlled using functions -sine and cosine- with annual and six-monthly periodicities, days of the week were also introduced in the models. The chemical air pollutants (PM2.5 and PM10, O3 and NO2) and the noise levels (Leqd and Leqn) were introduced into the model as linear
Subjects and exposure characteristics
A total of 298,705 births occurred in hospitals of Madrid City during the years 2001–2009. A figure of 24,620 was preterm births (8.2%). A figure of 20,442 was “very preterm births” (6.8%) and a figure of 4,178 was “extremely preterm births” (1.4%).
In the period analysed, the WHO value for daily PM2.5 concentrations, it has been surpassed 329 days (10.0%), for PM10, 446 days, and it represents 13.6%. For NO2 values, the WHO guidelines are for annual means, for this pollutant the value has been
Environmental exposure and births
Table 2 shows the results of Poisson models, through Relative Risk (RR) and Attributable Risk (AR), for Total births and Preterm births, separately. In the table, can be observed that in both neonatal outcomes, the concentration of PM2.5 at short-term (Lag 0 and Lag 1 for preterm) was statistically significant (p<0.05). In the same way, the variable Leqd corresponding to levels of diurnal noise was also statistically significant (p<0.05) for both neonatal outcomes at Lag 0. The impact of PM2.5
Discussion
This study was done to examine for first time in Madrid City whether maternal exposure to ambient variables as air pollutants, acoustic levels and temperature could be important contributors to increase at short-term the number of total born, as well as to increase the risk of born before 37 weeks.
Our findings suggest that exists effect of air pollutants, particularly PM2.5, and noise diurnal levels in both the total number of births and preterm births. Traffic may affect pregnancy outcomes to
Conclusion
Despite limitations, we observed evidence of a short term effect at Lag 0 (the same day), for the environmental variables analyzed, PM2.5 and O3 concentrations and diurnal noise level for the total number of births, and besides these, heat temperatures at Lag 1 (the preceding day, one day before birth) on preterm births in Madrid City during the studied period. The public health impact of air pollutants, noise levels and temperature on reproductive outcomes may be considerable, due to
Acknowledgments
This study was funded by a “Miguel Servet type 1” grant: SEPY 1037/14 (Cristina Linares Gil /Cristina Ortiz Burgos) and a FIS Project ENPY 1001/13 (Julio Díaz Jiménez /Rocío Carmona Alférez) from the Carlos III Institute of Health.
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