Table 2.

Adjusted odds ratios (ORs) [95% confidence intervals (CIs)] of preterm birth.^a

Variable	95% CI
	Unadjusted model	Adjusted model 1b	Adjusted model 2c	Adjusted model 3d
UFP
Quartile 1 ($<\mathrm{5,340}\text{particles}/\text{cc}$)	Ref	Ref	Ref	Ref
Quartile 2 (5,340–8,600 particles/cc)	1.17 (1.11, 1.22)	1.01 (0.96, 1.07)	1.03 (0.98, 1.08)	1.03 (0.98, 1.08)
Quartile 3 (8,600–14,600 particles/cc)	1.27 (1.22, 1.33)	1.05 (1.00, 1.10)	1.08 (1.02, 1.13)	1.08 (1.02, 1.13)
Quartile 4 ($>\mathrm{14,600}\text{particles}/\text{cc}$)	1.32 (1.27, 1.39)	1.11 (1.05, 1.16)	1.16 (1.10, 1.22)	1.14 (1.08, 1.20)
${\mathrm{NO}}_2$
Quartile 1 ($<21.8\text{ppb}$)	—	—	Ref	Ref
Quartile 2 ($21.8–23.8\text{ppb}$)	—	—	1.10 (1.05, 1.15)	1.10 (1.05, 1.16)
Quartile 3 ($23.9–25.5\text{ppb}$)	—	—	1.10 (1.05, 1.16)	1.11 (1.05, 1.15)
Quartile 4 ($>25.5\text{ppb}$)	—	—	1.15 (1.09, 1.21)	1.15 (1.09, 1.22)
Exposed to noise $>65\text{dB}$ CNEL	—	—	—	1.10 (1.01, 1.19)

Note: —, Data not available; CNEL, community noise equivalent level; dB, decibels; ppb, parts per billion; Ref, reference.

^aPTB $\text{cases}n=\mathrm{15,134}$.

^bAdjusted for maternal age, maternal educational attainment, SES, maternal race, and cigarette smoking. Educational attainment was recorded in 9 ordinal categories: No formal education, 8th grade or less, 9th grade through 12th grade with no diploma, high school graduate or GED, some college credit with no degree, associate’s degree, bachelor’s degree, master’s degree, doctorate or professional degree.

^cAdjusted for all variables in Adjusted Model 1 and ${\mathrm{NO}}_2$.

^dAdjusted for all variables in Adjusted Model 2 and airport noise.