Skip to main content

Table 2 Pooled associations between PM2.5 exposure (per 10 μg/m3 increment) during pregnancy and preterm birth risks in different subgroups

From: The association between fine particulate matter exposure during pregnancy and preterm birth: a meta-analysis

Subgroups No. of studies Heterogeneity test Summary OR (95 % CI) Hypothesis test I2 (%) Egger’s test
Q P Z P t P
Exposure during the entire pregnancy 13 80.51 <0.001 1.13* (1.03–1.24) 2.59 0.010 91.4 2.20 0.051
Specific trimester          
 First trimester exposure 10 89.14 <0.001 1.08 (0.92–1.26) 0.96 0.334 91.3 0.68 0.517
 Second trimester exposure 5 138.69 <0.001 1.09 (0.82–1.44) 0.60 0.548 98.7 0.311 0.776
 Third trimester exposure 9 44.83 <0.001 1.08** (0.99–1.17) 1.70 0.089 92.1 1.58 0.157
 First month of gestation 3 22.03 <0.001 1.10 (0.92–1.30) 1.03 0.301 91.0 0.58 0.666
 Within one month before birth 6 51.49 <0.001 1.01 (0.86–1.19) 0.09 0.926 96.8 0.03 0.980
Exposure assessment methoda          
 Individual exposure 3 4.94 0.085 1.11 (0.89–1.37) 0.93 0.352 61.3 1.74 0.332
 Semi-individual exposure 9 55.86 <0.001 1.14 (0.97–1.35) 1.56 0.119 93.0 0.35 0.737
 Regional level 4 46.19 <0.001 1.07 (0.94–1.23) 1.00 0.319 93.8 0.11 0.921
Study designa          
 Retrospective studies 9 70.98 <0.001 1.10* (1.01–1.21) 2.12 0.034 93.3 2.31 0.055
 Prospective studies 4 4.64 0.201 1.42* (1.08–1.85) 2.52 0.012 39.5 0.10 0.927
Study settinga          
 USA 8 50.49 <0.001 1.16* (1.05–1.29) 2.73 0.006 90.6 1.80 0.121
 Others 5 7.90 0.095 0.98 (0.95–1.01) 1.11 0.268 0.1 1.62 0.205
  1. a: All of these subgroup analyses were conducted for the studies that assessed the association between PM2.5 exposure during the entire pregnancy and preterm birth. All of these estimates were ORs for each 10 μg/m3 increment of PM2.5 exposure during the entire pregnancy
  2. *: p < 0.05
  3. **: 0.05 < p < 0.10
\