Meta-analyses of spontaneous abortion, summary risk estimate (SRE) by exposure category for all studies, sensitivity analyses and final result from higher validity studies
| (1) Light lifting or <12 kg | (2) Lifting unspecified weight or ≥5 kg |
(3) Heavy lifting or ≥10 kg,
≤10x per day or rarely | (4) Heavy lifting or ≥10 kg, unspecified frequency or ≥1x per day | (5) Heavy lifting or≥10 kg, ≥10x per day or often | |||||||||||
| N | SRE | (95% CI) | N | SRE | (95% CI) | N | SRE | (95% CI) | N | SRE | (95% CI) | N | SRE | (95% CI) | |
| All studies | 2 | 0.92 | (0.89 to 0.95) | 10 | 1.41 | (1.07 to 1.87)* | 9 | 1.00 | (0.82 to 1.21) | 11 | 1.13 | (1.00 to 1.28)* | 7 | 1.28 | (1.00 to 1.64)* |
| Sensitivity analyses | |||||||||||||||
| Developed countries and study period >1975 | 2 | 0.92 | (0.89 to 0.95) | 8 | 1.11 | (1.04 to 1.87)* | 6 | 1.07 | (0.95 to 1.22) | 8 | 1.19 | (1.06 to 1.33)* | 5 | 1.20 | (1.01 to 1.44)* |
| Response rate ≥80% | 2 | 0.92 | (0.89 to 0.95) | 6 | 1.12 | (1.04 to 1.20)* | 6 | 1.12 | (0.95 to 1.31) | 7 | 1.18 | (1.04 to 1.35)* | 5 | 1.36 | (0.88 to 2.11) |
| Prospective assessment of exposure | 1 | 0.97 | (0.53 to 1.78) | 4 | 1.11 | (1.03 to 1.19)* | 2 | 1.07 | (0.77 to 1.48) | 4 | 1.25 | (1.07 to 1.46)* | 2 | 1.31 | (1.17 to 1.47)* |
| Quantitative definition of lifting (weight, frequency) | 1 | 0.97 | (0.53 to 1.78) | 2 | 1.07 | (0.68 to 1.68) | 6 | 1.03 | (0.91 to 1.17) | 3 | 1.38 | (1.13 to 1.69)* | 5 | 1.21 | (0.86 to 1.69) |
| Adequate control of personals factors | 2 | 0.92 | (0.89 to 0.95) | 6 | 1.25 | (0.90 to 1.73) | 5 | 0.90 | (0.68 to 1.20) | 5 | 1.21 | (0.97 to 0.51) | 4 | 1.30 | (1.17 to 1.45)* |
| Adequate control of other occupational exposures | 0 | 3 | 1.38 | (0,94 to 2.03) | 2 | 1.05 | (0.88 to 1.25) | 2 | 1.20 | (1.00 to 1.44)* | 3 | 1.32 | (1.18 to 1.46)* | ||
| Final result | |||||||||||||||
| From studies with validity score >12 | 1 | 0.97 | (0.53 to 1.78) | 6 | 1.16 | (0.90 to 1.49) | 1 | 1.11 | (0.77 to 1.58) | 1 | 1.16 | (0.76 to 1.78) | 2 | 1.31 | (1.17 to 1.47)* |
| Test of heterogeneity†: Q, p-value (p), I2 | Q=0.03, p=0.86†, I2=0%† | Q=1.70, p=0.89, I2=0% | Q=20.14, p=0.01†, I2=60%† | Q=29.19, p<0.01†, I2=66%† | Q=0.61, p=0.43, I2=0% | ||||||||||
Final results, from high validity studies, are in bold.
*P-value <0.05
†Calculated for all studies if only one study has a validity score >12.