[Prenatal exposure to outdoor air pollution and preterm birth: a Meta-analysis].

To assess the association between exposure to prenatal outdoor air pollution and preterm birth to provide evidence in setting up programs for prevention on premature birth.Case-control studies regarding association between pregnant exposure to outdoor air pollution and preterm birth were collected. Data were analyzed with Stata 12.0.Ten articles including 48 556 cases and 548 495 controls were qualified for inclusion. RESULTS from Meta-analyses showed pooled ORs for exposure to NO2, PM10, CO, PM2.5, and NO during the entire pregnancy were 0.960 (95%CI: 0.935-0.985), 1.068 (95%CI: 1.035-1.103), 1.122 (95%CI: 1.078-1.168), 1.110 (95% CI: 1.043-1.181) and 0.994 (95% CI: 0.973-1.016). Association between air pollution and preterm birth varied with the periods of exposure. Pooled ORs for NO2, PM10 and SO2 exposure during the first trimester were 1.117 (95%CI: 1.052-1.186), 0.968 (95%CI: 0.812-1.153) and 1.258 (95%CI: 0.758-2.089). Pooled ORs for NO2, PM10, SO2 exposure during the second trimester were 1.000 (95% CI: 0.982-1.019), 1.127 (95% CI: 0.896-1.416) and 0.977 (95% CI: 0.711-1.342). Pooled ORs for NO2, PM10, SO2 exposure during the third trimester were 1.006 (95%CI: 1.002-1.010), 1.053 (95% CI: 0.973-1.139) and 1.003 (95% CI: 1.000-1.006).Exposures to PM10, CO and PM2.5 during the entire pregnancy, to NO2 during the first trimester, or to NO2 and SO2 during the third trimester were associated with preterm births.