PM_2.5 and NO₂ exposure during pregnancy and measures of fetal size and attained size at birth

Air pollution exposure during pregnancy has been associated with reduced fetal size and birth weight, but the sensitive exposure windows for these associations are not well established. We examined the association between gestational air pollution exposure and altered fetal size (femur length, biparietal diameter, head circumference, abdominal circumference, estimated fetal weight), measured in mid-pregnancy (week 20) and late-pregnancy (week 34), and attained size at birth (Z-scores of birth weight, length, and head circumference). Within the UPSIDE cohort study (N = 312 pregnant women) in Rochester, New York, we estimated residential, daily, ambient PM_2.5 and NO₂ concentrations using a spatial-temporal model. Distributed lag models estimated increases/decreases in each marker associated with interquartile range (IQR) increases in gestational week mean PM_2.5 (3 μg/m³) and NO₂ (9 ppb) concentrations, adjusting for child sex, maternal pre-pregnancy body mass index, race/ethnicity, and smoking during pregnancy. For birth measures, gestational age at birth was also included. Each IQR increase in NO₂ in gestational weeks 18-33 was associated with decreased femur length at week 34 (-1.18 mm; 95% CI = -2.09, -0.27). However, each IQR increase during gestational weeks 8-9 was associated with increased femur length at week 20 (0.05 mm; 95% CI = 0.00, 0.09). No associations were observed between weekly NO₂/PM_2.5 concentrations and other fetal size or birth measures in models using all participants' data. NO₂/femur length associations differed by child sex. Thus, there was limited support for an association between gestational PM_2.5/NO₂ exposure and ultrasound measures of fetal size in mid- and late- pregnancy.