Multiple pregnancies and air pollution in moderately polluted cities: Is there an association between air pollution and fetal growth?

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Background: Multiple pregnancies (where more than one fetus develops simultaneously in the womb) are systematicallyexcluded from studies of the impact of air pollution on pregnancy outcomes. This study aims toanalyze, in a population of multiple pregnancies, the relationship between fetal growth restriction (FGR), smallfor gestational age (SGA) and exposure to air pollution in moderately polluted cities.Methods: All women with multiple pregnancies living in the city of Besançon or in the urban area of Dijon andwho delivered at a university hospital between 2005 and 2009 were included. FGR and SGA were obtained frommedical records. Outdoor residential nitrogen dioxide (NO2) exposure was assessed using the mother's address,considering a 50m radius buffer over the following defined pregnancy periods: each trimester, entire pregnancyand two months before delivery. Logistic regression analyses were performed.Results: This study included 249 multiple pregnancies with 506 newborns. The median of NO2 concentrationconsidering a 50m radius buffer during entire pregnancy was 23.1 μg/m3 (minimum at 10.1 μg/m3 and maximumat 46.7 μg/m3). No association was observed between NO2 and SGA whatever the pregnancy period (theodds ratio (OR) range 0.78 to 0.88). Regarding FGR, the OR associated with an increase of 10 μg/m3 of NO2exposure during entire pregnancy was 1.52 (95% Confidence Interval (CI): 1.02–2.26). Similar results wereobserved for NO2 exposure during the various pregnancy periods.Conclusions: These results are in line with an association between NO2 and fetal growth in multiple pregnanciesfor an exposure mostly below the threshold set out in European legislation.