The impact of prenatal exposure to PM2.5 on childhood asthma and wheezing: a meta-analysis of observational studies.

With the accelerated pace of economic development and modernization, air pollution has become one of the most focused public health problems. However, the impact of particulate matter exposure during pregnancy on childhood asthma and wheezing remains controversial. We performed this meta-analysis to explore the relationship between prenatal exposure to PM2.5 and childhood asthma and wheezing. Candidate papers were searched on PubMed, Web of Science, Embase, and Cochrane Library before July 15, 2019. The main characteristics of the included studies were extracted, and the quality was evaluated by the Newcastle-Ottawa Scale (NOS). A sensitivity analysis was performed to assess the impact of individual studies on the combined effects. The Egger and Begg tests were conducted to examine the publication bias. Nine studies were included in the final analysis. Prenatal exposure to PM2.5 significantly increased the risk of childhood asthma and wheezing (OR = 1.06, 95% CI 1.02-1.11; per 5 μg/m3). Maternal exposure was more strongly related to childhood asthma and wheezing before age 3 (OR = 1.15, 95% CI 1.00-1.31; per 5 μg/m3) than after (OR = 1.04, 95% CI 1.00-1.09; per 5 μg/m3). Children in developed countries showed more severe effects (OR = 1.14, 95% CI 1.02-1.27; per 5 μg/m3). Children who were born to mothers with higher levels of prenatal exposure were at higher risk of asthma and wheezing (OR = 1.07, 95% CI 1.02-1.13; per 5 μg/m3). This meta-analysis indicated that the impact of PM2.5 on childhood asthma and wheezing begins as early as utero, so regulating pollutant emission standards and strengthening prenatal protection are crucial to maternal and child health.