Table 3.

Adjusted^a ORs and 95 % CIs for the association between a 10-unit increase in maternal exposure to ambient levels of PM_2.5 (μg/m³) and moderately, mildly and severely PTBs and term SGA in Harris County, TX, 2005–2007, excluding infants with birth defects (n = 171,923)

Period of pregnancy (weeks)	Severely PTBs (n = 1,188) OR [95 % CI]	Moderately PTBs (n = 1,701) OR [95 % CI]	Mildly PTBs (n = 14,397) OR [95 % CI]	SGA (n = 16,520) OR [95 % CI]
1–4	1.89 [1.33, 2.68]	1.91 [1.44, 2.54]	1.16 [1.05, 1.28]	1.04 [0.94, 1.14]
5–8	0.90 [0.60, 1.33]	1.09 [0.78, 1.52]	1.08 [0.96, 1.21]	0.98 [0.88, 1.10]
9–12	1.27 [0.87, 1.87]	1.64 [1.18, 2.28]	1.26 [1.12, 1.1]	1.09 [0.98, 1.22]
13–16	0.71 [0.49, 1.03]	0.96 [0.71, 1.32]	0.96 [0.86, 1.07]	1.05 [0.95, 1.17]
17–20	1.69 [1.15, 2.50]	0.92 [0.67, 1.27]	1.16 [1.03, 1.30]	0.87 [0.78, 0.98]
21–24	–	0.88 [0.64, 1.21]	0.83 [0.74, 0.93]	1.11 [0.98, 1.23]
25–28	–	1.93 [1.43, 2.60]	1.10 [0.99, 1.23]	1.01 [0.92, 1.12]
29–32	–	–	1.30 [1.17, 1.46]	1.01 [0.91, 1.12]
33–36	–	–	–	0.94 [0.84, 1.04]

OR odds ratio, CI confidence intervals, SGA small for gestational age, WIC Women, Infants, and Children, BMI body mass index

^aAdjusted for pollutant concentrations during the other 4-week periods, season, race, level of education, age, BMI status, support received from infant’s father, receipt of WIC services; trimester prenatal care initiated; parity; and type of payment for delivery