Preconception and gestational versus postnatal exposure to air pollutants and risk of autism spectrum disorder: a systematic review and meta-analysis.

Purpose: The rising prevalence of ASD has prompted extensive research into potential environmental risk factors, with air pollution particularly emerging as a major concern. A systematic review and meta-analysis on the effect of air pollutants and time of exposure (particularly, PM, PM, NO, and O) and the risk of ASD was therefore performed.

Methods: Following PRISMA guidelines and PROSPERO registration (Ref: CRD42023464592), a thorough literature search was conducted across multiple databases, including Scopus, PubMed/MEDLINE, Embase, PsycINFO, Web of Science, and Cochrane Library. The analysis included 27 studies encompassing 369,460 participants, 47,973 of whom were diagnosed with ASD.

Results: Preconception exposure to air pollutants showed a protective trend for PM, PM, and O with a 10%, 5%, and 19% reduced risk of ASD, whereas NO had a 28% higher likelihood of ASD. During gestation, PM exposure increased ASD risk by 15%, with 13% and 9%, 25% and 7%, and 25% and 10% increases in ASD risk with PM and NO for the first, second, and third trimesters, respectively. In the first year of life, 20%, 8%, 33%, and 14% increases in risk were found for PM, PM, NO, and O, respectively, while such risk estimates increased to 179%, 60%, 12%, and 179% for the second year of life.

Conclusions: In this meta-analysis, the relationships between air pollutants and ASD risk revealed significant associations, particularly for PM and NO. Exposure during preconception exhibited a protective trend, while postnatal exposure, particularly during the second year of life uncovered substantially higher ASD risk.