Exposure to pollution during pregnancy can have many adverse effects in infants and children that can even extend into adulthood. For example, air pollution exposure is associated with increased risk of low birth weight, preterm birth and risk for developing asthma later in life. Much of this is due to the fast pace of fetal growth and development; however, the exact ways pollutants have these effects and the roles of genes related to immune function and stress response are not fully understood.