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 | Â | Â | Â | Â | Â | Â | Â | Â | Â |
 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 | Â | Â | Â | Â | Â | Â | Â | Â | Â |
 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 | Â | Â | Â | Â | Â | Â | Â | Â | Â |
 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 | Â | Â | Â | Â | Â | Â | Â | Â | Â |
 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 |