Exposure to [Formula: see text] during Pregnancy and Fetal Growth in Eastern Massachusetts, USA

BACKGROUND: Prior studies have examined the association between fine particulate matter [PM [Formula: see text] in aerodynamic diameter ([Formula: see text])] and fetal growth with either limited spatial or temporal resolution. OBJECTIVES: In this study, we examined the association between [Formula: see text] exposure during pregnancy and fetal growth measures (ultrasound parameters and birth weight) in a pregnancy cohort using spatiotemporally resolved [Formula: see text] in Eastern Massachusetts, USA. METHODS: We used ultrasound measures of biparietal diameter (BPD), head circumference, femur length, and abdominal circumference (AC), in addition to birth weight, from 9,446 pregnancies that were delivered at the Beth Israel Deaconess Medical Center from 2011–2016. We used linear mixed-effects models to examine the associations of [Formula: see text] in two exposure windows (the first 16 wk of pregnancy and the cumulative exposure up until the assessment of fetal growth) with anatomic scans (ultrasound [Formula: see text]), growth scans (ultrasound [Formula: see text]), and birth weight. All models were adjusted for sociodemographic characteristics, long-term trends, and temperature. RESULTS: Higher [Formula: see text] exposure in the first 16 wk was associated with smaller fetal growth measures, where associations were particularly strong for BPD, AC, and birth weight. For example, a [Formula: see text] increase in [Formula: see text] was associated with a lower mean BPD [Formula: see text]-score of [Formula: see text] (95% CI: [Formula: see text] , [Formula: see text]) before 24 wk, a lower mean AC [Formula: see text]-score of [Formula: see text] (95% CI: [Formula: see text] , [Formula: see text]) after 24 wk, and a lower mean birth weight [Formula: see text]-score of [Formula: see text] (95% CI: [Formula: see text] , [Formula: see text]). Analyses examining the associations with cumulative [Formula: see text] exposure up until the assessment of fetal growth produced attenuated associations. CONCLUSIONS: Higher gestational exposure to [Formula: see text] was associated with smaller fetal growth measures at levels below the current national standards. https://doi.org/10.1289/EHP9824