Ambient air pollution and fetal growth restriction: Physician diagnosis of fetal growth restriction versus population-based small-for-gestational age.

BACKGROUND: Ambient air pollution may affect fetal growth restriction (FGR) through several mechanisms. However, prior studies of air pollution and small-for-gestational age (SGA), a common proxy for FGR, have reported inconsistent findings.

OBJECTIVE: We assessed air pollution in relation to physician-diagnosed FGR and population-based SGA in the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Consecutive Pregnancy Study (2002-2010).

METHODS: Among 50,005 women (112,203 singleton births), FGR was captured from medical records and ICD-9 codes, and SGA determined by population standards for birthweight <10th, <5th and <3rd percentile. Community Multiscale Air Quality models estimated ambient levels of seven criteria pollutants for whole pregnancy, 3-months preconception, and 1st, 2nd and 3rd trimesters. Generalized estimating equations with robust standard errors accounted for interdependency of pregnancies within participant. Models adjusted for maternal age, race/ethnicity, pre-pregnancy body mass index, smoking, alcohol, parity, insurance, marital status, asthma and temperature.

RESULTS: FGR was diagnosed in 1.5% of infants, and 6.7% were <10th, 2.7% <5th and 1.5% <3rd percentile for SGA. Positive associations of SO, NO and PM and negative associations of O with FGR were observed throughout preconception and pregnancy. For example, an interquartile increase in whole pregnancy SO was associated with 16% (95% CI 8%, 25%) increased FGR risk, 17% for NO (95% CI 9%, 26%) and 12% for PM (95% CI 6%, 19%). Associations with SGA were less clear.

CONCLUSIONS: Chronic exposure to air pollution may be associated with FGR but not SGA in this low-risk population.