Background: Air pollution exposure has been associated with reduced fetal growth and birth-size with changes in placental vascular structure proposed as mediators of this association. Previously, we reported that early-pregnancy NO2 exposure was associated with altered chorionic surface arterial vasculature in pregnant Rochester, NY residents.

Objective: We examined associations between gestational-week residential PM2.5 and NO2 concentrations and increases/decreases in placental chorionic surface vasculature in pregnancies of Pittsburgh, PA residents.

Methods: Using placenta photographs from term deliveries of 51 pregnant women in the Magee-Women’s Research Institute cohort, we estimated 17 chorionic plate surface vessel outcomes. We used distributed lag models to determine if/when gestational week (0–37) PM2.5 and NO2 concentrations were associated with each outcome.

Results: Each 4-ppb increase in PM2.5 during weeks 8–22 and 6-19 was associated with decreased mean arc length (-0.30 cm; 95% CI = -0.57, -0.04) and decreased standard deviation of arc length (-0.26 cm; 95% CI = -0.50, -0.03) respectively. PM₂.₅ during weeks 16-28 was associated with decreased mean tortuosity (-0.02; 95% CI = -0.03, 0.00). During weeks 4-16 and 14-24 weeks, PM2.5 was associated with decreased arterial-end to venous-end distance (-0.01 cm; 95% CI = -0.02, 0.00) and mean artery-vein distance (-0.10 cm; 95% CI= -0.18, -0.02), respectively. Each 4-ppb increase in NO2 during weeks 0-10 was associated with increased mean distance from arterial endpoint to venous endpoint (0.07 cm; 95% CI: 0.04, 0.10).

Conclusion: Although we had limited sample size, we found associations between early- and mid-pregnancy PM2.5 and NO2 and changes in arterial length, variability in length, and arterial branching in the placenta. These findings suggest altered placental angiogenesis and vascular development is associated with increased residential air pollution exposure during pregnancy.