This review provide concise and precise updates on the latest progress made in the area of research aimed at the association between prenatal air pollution exposure and birth weight of neonates. Especially it focuses on the critical windows of prenatal exposure, potentially sensitive populations such as male fetuses, fetuses of multiparous and smoking mothers, and mothers above 35 years of age. The article also describes the methodological challenges for future research in the area of environmental epidemiology, like controlling of confounding, assessing the individual exposure or problem of simultaneous exposure to many pollutants.