Motor vehicle traffic emissions are the single largest contributor to ambient air pollution in many developed countries and it has been suggested that these emissions can affect outcomes of pregnancy. An individual's exposure experience is greatly influenced by where they live as emission concentrations are much higher closer to roads. A systematic review was conducted using the MOOSE guidelines in order to synthesise studies published 1989-2009 which investigated pregnancy outcomes in relation to residential exposure to traffic emissions. Twelve studies met the inclusion criteria and were consequently reviewed. We identified exposure assessment methods and the scope of health endpoints that have been investigated. Gestational duration, intrauterine growth, mortality and pregnancy complications have been studied using simple distance, distance-weighted traffic density, annually averaged daily traffic counts, dispersion models and land-use regression models. Few studies investigated mortality and pregnancy complications and no study investigated the risk of congenital anomalies. The evidence to date suggests an adverse effect was consistently reported for gestational duration and less consistently reported yet plausible for intrauterine growth. However, the small number of studies, the possibility of publication bias and the limited research conducted on biological mechanisms precluded more formal statements on the existence of an effect. The ubiquity of motor vehicle traffic emissions, the biological vulnerability of the fetus, and the adverse associations detected among many of the twelve reviewed studies motivates a multidisciplinary collaborative effort toward further research on the topic
