Abstract
Prenatal exposure to airborne particles is a potential risk factor for infant neuropsychological development. This issue is usually explored by regression analysis under the implicit assumption that all relevant confounders are accounted for. Our aim is to estimate the causal effect of prenatal exposure to high concentrations of airborne particles with a diameter < 2.5 µm (PM2.5) on children’s psychomotor and mental scores in a birth cohort from Gipuzkoa (Spain), and investigate the robustness of the results to possible unobserved confounding. We adopted the propensity score matching approach and performed sensitivity analyses comparing the actual effect estimates with those obtained after adjusting for unobserved confounders simulated to have different strengths. On average, mental and psychomotor scores decreased of −2.47 (90% CI: −7.22; 2.28) and −3.18 (90% CI: −7.61; 1.25) points when the prenatal exposure was ≥17 μg/m3 (median). These estimates were robust to the presence of unmeasured confounders having strength similar to that of the observed ones. The plausibility of having omitted a confounder strong enough to drive the estimates to zero was poor. The sensitivity analyses conferred solidity to our findings, despite the large sampling variability. This kind of sensitivity analysis should be routinely implemented in observational studies, especially in exploring new relationships.
Highlights
Many studies around the world documented long term and short term effects of air pollution on population mortality and morbidity [1,2]
Our results suggest that prenatal exposure to average levels of PM2.5 ≥ 17 μg/m3 had a negative effect on a child’s mental and psychomotor development at around 15 months of age, even if the confidence intervals of the effects estimates were wide, reflecting large sampling variability
In interpreting the results of the sensitivity analysis, we focused on the point estimates of the effects and not on the confidence intervals limits as sometimes suggested [11,12]
Summary
Many studies around the world documented long term and short term effects of air pollution on population mortality and morbidity [1,2]. Several researches focused on the effects of prenatal exposures to air pollution on children’s neuropsychological development [3]. Harris et al [4] analyzed. 1109 mother–child pairs from Eastern Massachusetts (USA) concluding that parental proximity to major roadways may negatively influence performance across a range of mental domains in childhood. Guxens et al [5] found significant associations between high levels of nitrogen dioxide (NO2 ) and benzene and infant neurodevelopment in the Spanish cohorts participating in the INMA (Infancia y Medio Ambiente, the Spanish for Childhood and Environment) Project. Public Health 2019, 16, 4381; doi:10.3390/ijerph16224381 www.mdpi.com/journal/ijerph
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