Air Pollution and Birth Weight: New Clues about a Potential Critical Window of Exposure

Researchers have previously reported associations between exposure to air pollution during pregnancy and decreased birth weights.1,2 However, in any given location there is usually very little variation in air pollutant concentrations over short time periods, barring events such as wildfires and other seasonally influenced sources of pollution. It has therefore been difficult to pinpoint a particular window of time during gestation when an exposed fetus might be particularly susceptible to air pollutants. In this issue of EHP, investigators report findings on birth weight arising from a unique research opportunity: the temporary decline in air pollution during the 47 days comprising the 2008 Beijing Summer Olympic Games and Paralympic Games.