<p>Poor fetal growth is associated with adverse postnatal health outcomes. In the newborn period, compared with well-grown infants, those small-for-gestational age (typically defined as less than 10th percentile are at higher risk of mortality and morbidities including difficulties with glucose homeostasis and thermoregulatory control. They are also more likely to require neonatal intensive care. Subsequently, small-for-gestational age infants are predisposed to hypertension and neurodevelopmental delays and disabilities. The etiology of poor fetal growth is multifactorial. Maternal conditions such as pre-eclampsia, infections such as cytomegalovirus and toxoplasmosis, maternal malnutrition and exposures to environmental pollutants such as lead, can all lead to infants being born smaller than their genetic potential.</p>

<p>Maternal cigarette smoking in pregnancy represents one of the most preventable causes of poor fetal growth. Air pollution, which contains many of the same compounds found in cigarette smoke including fine particulate matter smaller than five microns in diameter (PM_2.5), has been shown to increase the risk of many of the same conditions caused by smoking including lung cancer and cardiovascular disease. Further, air pollution exposure in pregnancy is associated with lower birth weight for gestational age. How air pollution affects fetal growth is incompletely understood, but new insights into how the fetal epigenome responds to cigarette smoke may provide clues as to how air pollution may affect the developing fetus.</p>