Table 1 Meta-analysis summary pooled estimates for the effect of overall and subgroups of tobacco use on each growth outcome at birth
| Â | No. of studies | No. of associations | Pooled estimates | Heterogeneity | ||
|---|---|---|---|---|---|---|
X2 | P | I 2 | ||||
SGA at birth | Â | Â | AOR a (95% CI) | Â | Â | Â |
 All tobacco use (all of the below) | 71 | 168 | 1.95 (1.76, 2.16) | 21253.97 | <0.001 | 99.2% |
 Quit during pregnancy | 14 | 25 | 1.17 (0.95, 1.44) | 458.62 | <0.001 | 94.8% |
 Ever smoked during pregnancy | 52 | 70 | 2.17 (1.82, 2.60) | 17475.92 | <0.001 | 99.6% |
 Smoked 1-10 cigarettes/day | 22 | 34 | 1.69 (1.59, 1.79) | 118.70 | <0.001 | 72.2% |
 Smoked >10 cigarettes/day | 23 | 37 | 2.53 (2.31, 2.78) | 267.16 | <0.001 | 86.9% |
Length at birth | Â | Â | WMD b (95% CI) | Â | Â | Â |
 All tobacco use (all of the below) | 47 | 72 | 0.43 (0.41, 0.44) | 1157.71 | <0.001 | 93.9% |
 Quit during pregnancy | 4 | 4 | -0.11 (-0.22, -0.01) | 2.02 | 0.569 | 0.0% |
 Ever smoked during pregnancy | 40 | 44 | 0.46 (0.44, 0.48) | 969.73 | <0.001 | 95.6% |
 Smoked 1-10 cigarettes/day | 7 | 7 | 0.30 (0.21, 0.38) | 15.56 | 0.016 | 61.4% |
 Smoked >10 cigarettes/day | 8 | 10 | 0.51 (0.37, 0.65) | 34.87 | <0.001 | 78.6% |
Head circumference at birth | Â | Â | WMD b (95% CI) | Â | Â | Â |
 All tobacco use (all of the below) | 43 | 71 | 0.27 (0.25, 0.29) | 707.87 | <0.001 | 90.1% |
 Quit during pregnancy | 5 | 5 | 0.01 (-0.08, 0.11) | 3.25 | 0.517 | 0.0% |
 Ever smoked during pregnancy | 37 | 41 | 0.28 (0.26, 0.30) | 631.13 | <0.001 | 93.7% |
 Smoked 1-10 cigarettes/day | 7 | 7 | 0.17 (0.08, 0.25) | 5.04 | 0.539 | 0.0% |
 Smoked >10 cigarettes/day | 8 | 11 | 0.35 (0.25, 0.45) | 24.40 | 0.010 | 54.9% |