Prenatal exposure to PM2.5 and NO2 and sex-dependent infant cognitive and motor development

Background. Prenatal exposure to air pollutants including particulate matter (< 2.5 mu m of diameter,PM2.5)and nitrogen dioxide (NO2) has been identified as a potential risk factor for neuropsychological developmental and mental health disorders. Objective: This study aimed to analyze the associations between prenatal PM2.5 and NO2 exposure and cognitive functions in children at 4-6 years of age, including sex differences, and the modification effect of the duration predominant breastfeeding these associations. Design: This study was conducted as part of the INMA project, a population-based birth cohort study in Spain (n = 1119). Each of the pregnant mothers was assigned a prenatal exposure to PM2.5 and NO2 for their whole pregnancy based on their place of residence. At the 4-6 year-old follow-up, infants' neuropsychological development was assessed using McCarthy scales: Verbal, Perceptive-Manipulative, Numeric, General Cognitive, Memory and Motor (gross and fine). Between 6 and 14 months of age, information concerning breastfeeding was gathered with a questionnaire. Regression analyses were performed to estimate the associations between exposure and outcomes, accounting for potential confounders. The analyses were stratified by child sex and breastfeeding duration. Results: The majority of coefficients for the different cognitive domains were negative either for PM2.5 and NO2, though none was statistically significant. After stratifying by sex, the associations become even more negative for boys, with some of the associations becoming statistically significant (memory both for PM2.5 and NO2), and global cognition and verbal for NO2. Duration of predominant breastfeeding was not found to have a modifying effect. Conclusions: These findings suggest a sex-dependent effects on neuropsychological development at 4-6 years of age, with a greater vulnerability in boys, specifically in domains related to memory, verbal and general cognition. No modifying effect was observed for duration of predominant breastfeeding.