Table 3.

Adjusted^a odds ratios (aOR) and 95% confidence intervals (CI) for preterm birth comparing highest quartile^b to lower 3 quartiles of each pollutant exposure during the last month and last 6 weeks of pregnancy in four counties in San Joaquin Valley, 2000–2006 (N=247,487).

Exposure	Gestational age weeks	N	Last month of pregnancy			N	Last six weeks of pregnancy
			aOR	95% CI			aOR	95% CI
CO	37–42	185,604	1.00	–	–	185,689	1.00	–	–
	34–36	4811	0.95	0.92	0.99	4850	0.97	0.93	1.00
	32–33	925	1.06	0.98	1.15	910	1.03	0.95	1.12
	28–31	626	0.89	0.80	0.99	633	0.9	0.81	1.00
	24–27	335	1.53	1.30	1.81	368	1.94	1.65	2.28
	20–23	163	2.23	1.78	2.80	150	1.86	1.48	2.33
NO2	37–42	215,810	1.00	–	–	215,817	1.00	–	–
	34–36	5941	0.98	0.95	1.01	6065	1.01	0.98	1.04
	32–33	1134	1.08	1.00	1.16	1114	1.04	0.96	1.12
	28–31	775	0.94	0.85	1.04	782	0.93	0.85	1.03
	24–27	351	1.15	0.98	1.35	392	1.39	1.19	1.62
	20–23	196	2.24	1.82	2.77	204	2.29	1.85	2.83
PM10	37–42	214,693	1.00	–	–	214,692	1.00	–	–
	34–36	5612	0.97	0.93	1.00	5577	0.96	0.93	1.00
	32–33	997	0.96	0.89	1.04	983	0.95	0.87	1.02
	28–31	664	0.79	0.72	0.88	662	0.83	0.75	0.92
	24–27	352	1.33	1.13	1.56	349	1.29	1.10	1.52
	20–23	170	1.93	1.56	2.4	194	2.49	2.02	3.08
PM2.5	37–42	214,513	1.00	–	–	214,549	1.00	–	–
	34–36	5366	0.98	0.94	1.01	5599	1.01	0.97	1.04
	32–33	1070	1.15	1.06	1.24	1094	1.16	1.08	1.25
	28–31	821	1.30	1.19	1.43	913	1.51	1.37	1.65
	24–27	400	2.05	1.75	2.39	421	2.19	1.87	2.55
	20–23	198	2.84	2.29	3.52	200	2.69	2.18	3.33

Abbreviations: aOR, adjusted odds ratio; CI, confidence interval

^aAdjusted for maternal age, education, race, infant birth weight, prenatal care initiation in first trimester, Medi-Cal payment of birth costs

^bCut-offs for highest quartile of exposure: CO 0.60 ppm; NO₂ 19.49 ppb; PMio 42.77 μg/m³; PM_2.5 20.75 μg/m³