INTRODUCTION

BACKGROUND OF THE STUDY

The knowledge about air pollution effects on birth weight, prematurity, and small for gestational age (SGA) in low-exposure areas is insufficient. Maternal Exposure

Air pollution is a key environmental and social issue of our time that, to a dierent extent, aects all regions, age and socio-economic groups. This poses multiple challenges in terms of management and mitigation of harmful pollutants (Viard et al., 2015). Indeed, the policy eorts and costs faced so far to reduce air pollution have been substantial (Fenger, 2009; Guerreiro et al., 2014), with many countries experiencing cleaner air. Despite these eorts, the concentration levels still exceed the recommended limits in many cities, especially for particulate matter (PM) (EEA, 2016). While the adverse health eects of air pollution in the adult population have been largely documented (Anderson, 2009), much less is known about the eects on infants and only few studies investigate the impacts of in utero exposure during pregnancy. Most contributions consider infant mortality as the main outcome, because of both high availability of mortality data on a large population scale and the relevance of infant mortality for policy development (Cesur et al., 2017, among others).1 Only few of them focus on less severe health outcomes at birth, which have been demonstrated to be a good proxy for individual performance later in life (Black et al., 2007). Indeed, studying the impact of prenatal pollution exposure on fetal health is important because the intra-uterine environment is a crucial determinant of infant's survival and health for the years to come. Previous studies include pre-term birth (PTB) and low birth weight (LBW) among risk factors for delays in motor and social development throughout early childhood (Hediger et al., 2002). They also show that neonates with low birth weight who survive infancy are at increased risk for health problems, among which disability (Elder et al., 2019), and death from ischemic heart disease (Barker et al., 1989). Finally, birth weight (BW) strongly aects child cognitive development (Figlio et al., 2014), predicts important socio-economic outcomes later in life such as annual earnings (Bharadwaj et al., 2017) and is also subject to intergenerational transmission (Currie and Moretti, 2007). Given that health shocks can impact human capital covering labor supply, productivity, and cognition, air pollution can be viewed as an important factor of production associated with economic growth. In this respect, the negative eects of poor health at birth on future child and adult outcomes stress the importance to identify the risk factors for fetal development (Currie, 2009), among which exposure to PM is an important one. Nevertheless, the causal evidence on the impact of PM on health outcomes at birth remains scant.2 The present paper addresses this issue by examining the impact of air pollution on infant health in Italy in the 2000s.

OBJECTIVES

The aim of this birth cohort study was to investigate whether low-level exposure to air pollution was associated with prematurity and fetal growth and whether there are sex-specific effects.Maternal Exposure

METHODOLOGY

We combined high-quality registry information on 81,110 births with individually modeled exposure data at residence for nitrogen oxides (NO(x)) and proximity to roads with differing traffic density. The data were analyzed by logistic and linear regression with and without potential confounders.Maternal Exposure

RESULTS: We observed an increased risk for babies being SGA when we compared highest and lowest NO(x) quartiles, adjusting for maternal age, smoking, sex, and year of birth. After additional adjustment for maternal country of origin and parity (which were highly intercorrelated), the increase was no longer statistically significant. However, in subgroup analyses when we compared highest and lowest NO(x) quartiles we still observed an increased risk for SGA for girls [odds ratio (OR)=1.12; 95% confidence interval (CI), 1.01-1.24); we also observed increased risk among mothers who had not changed residency during pregnancy (OR=1.09; 95% CI, 1.01-1.18). The confounders with the greatest impact on SGA were parity and country of origin. Concerning prematurity, the prevalence was lower in the three higher NO(x) exposure quartiles compared with the lowest category. Maternal Exposure

LIMITATIONS OF THE STUDY 

A limitation of this study is the use of survey research. There may be surveys returned that were not filled out truthfully or with responses that do not reflect true intentions. The results will not be generalizable beyond the population or sample used.