Table 3.

Odds ratios (95% confidence intervals) for preterm birth in association with interquartile range increase in urinary oxidative stress biomarkers by study visit.

Overall preterm birth
8-OHdG				8-Isoprostane
	N (cases, controls)	OR (95% CI)	p value	N (cases, controls)	OR (95% CI)	p value
Visit 1	123, 326	0.25 (0.14, 0.46)	<0.01	123, 326	1.72 (1.18, 2.51)	0.01
Visit 2	114, 289	0.21 (0.10, 0.42)	<0.01	114, 289	2.33 (1.44, 3.77)	<0.01
Visit 3	107, 282	0.44 (0.24, 0.81)	<0.01	107, 282	2.05 (1.31, 3.19)	<0.01
Visit 4	59, 294	0.45 (0.23, 0.90)	0.02	59, 294	1.76 (1.08, 2.88)	0.02
Spontaneous preterm birth
8-OHdG				8-Isoprostane
	N (cases, controls)	OR (95% CI)	p value	N (cases, controls)	OR (95% CI)	p value
Visit 1	54, 326	0.26 (0.12, 0.56)	<0.01	54, 326	2.72 (1.46, 5.06)	<0.01
Visit 2	52, 289	0.30 (0.13, 0.71)	<0.01	52, 289	7.10 (2.80, 18.0)	<0.01
Visit 3	47, 282	0.33 (0.14, 0.74)	<0.01	47, 282	4.45 (1.96, 10.1)	<0.01
Visit 4	24, 294	0.75 (0.28, 2.01)	0.57	24, 294	5.27 (1.82, 15.3)	<0.01
Placental preterm birth
8-OHdG				8-Isoprostane
	N (cases, controls)	OR (95% CI)	p value	N (cases, controls)	OR (95% CI)	p value
Visit 1	33, 326	0.21 (0.07, 0.58)	<0.01	33, 326	1.02 (0.62, 1.69)	0.93
Visit 2	29, 289	0.12 (0.04, 0.40)	<0.01	29, 289	1.19 (0.60, 2.34)	0.62
Visit 3	30, 282	0.40 (0.17, 0.94)	0.04	30, 282	0.79 (0.44, 1.43)	0.44
Visit 4	12, 294	0.19 (0.04, 0.85)	0.03	12, 294	0.59 (0.29, 1.19)	0.14

Abbreviations: 8-OHdG, 8-hydroxydeoxyguanosine; OR, odds ratio. Models adjusted for urinary specific gravity, maternal age, race/ethnicity, education level, health insurance provider, and pre-pregnancy body mass index (BMI).