Table 2.

Pooled associations between PM₁₀ exposure, NO₂ exposure and LBW in different subgroups

Subgroup	PM10			NO2
	n	I 2 (%)	OR (95% CI)	n	I 2 (%)		OR (95% CI)
Study setting
Non-Asian	9	74.0	1.07 (1.03–1.10)	8	45.3	1.02 (0.99–1.04)
Asian	2	30.2	0.87 (0.71–1.05)	3	0.0	1.09 (0.99–1.21)
Study design
Cohort study	8	72.2	1.06 (1.02–1.11)	9	39.8	1.02 (0.99–1.04)
Case-control study	3	81.8	1.04 (0.99–1.10)	2	0.0	1.04 (1.01–1.07)
Exposure type
Continuous	9	63.1	1.07 (1.04–1.11)	10	38.5	1.02 (1.00–1.04)
Categorical	2	0.0	0.87 (0.76–0.99)	1		1.06 (0.89–1.26)
Data source
Monitoring network data	7	75.1	1.05 (1.01–1.09)	7	44.5	1.01 (0.99–1.04)
Land use regression model based on monitoring network data	4	79.7	1.07 (1.00–1.14)	4	0.0	1.05 (1.02–1.08)
NOS
≤7	3	76.8	0.99 (0.93–1.04)	3	0.0	1.11 (1.03–1.20)
>7	8	62.3	1.07 (1.03–1.12)	8	31.7	1.01 (0.99–1.04)
Adjustment for smoking
Yes	6	68.6	1.07 (1.03–1.11)	5	48.0	1.07 (1.00–1.15)
No	5	78.0	1.03 (0.96–1.11)	6	2.8	1.02 (0.99–1.04)

n: number of effect estimates