Summary of key results from meta-analysis by outcome and exposure category
| Outcome | Exposure category | SRE (95% IC) | Statistical precision* | Sensitivity analyses† | Consistency‡ | Strength of evidence§ |
| SA | (1) Light lifting or <12 kg | 0.97 (0.53 to 1.78) | – | ± | + | Weak evidence of no association |
| (2) Lifting unspecified weight or ≥5 kg | 1.16 (0.90 to 1.49) | – | + | + | Weak evidence of positive association | |
| (3) Heavy lifting or ≥10 kg, ≤10x/day or rarely | 1.11 (0.77 to 1.58) | – | ± | – | Inconclusive data | |
| (4) Heavy lifting or ≥10 kg, unspecified frequency or ≥1x/day | 1.16 (0.76 to 1.78) | – | + | – | Inconclusive data | |
| (5) Heavy lifting or ≥10 kg, ≥10x/day or often | 1.31 (1.17 to 1.47) | + | + | + | Good evidence of positive association | |
| PTD | (1) Lifting <12 kg | 1.02 (0.86 to 1.23) | – | + | + | Weak evidence of no association |
| (2) Lifting unspecified weight or ≥5 kg | 1.04 (0.85 to 1.29) | – | ± | + | Weak evidence of no association | |
| (3) Heavy lifting or ≥10 kg, ≤10x/day or rarely | 0.95 (0.81 to 1.10) | ± | + | + | Moderate evidence of no association | |
| (4) Heavy lifting or ≥10 kg, unspecified frequency or ≥1x/day | 1.08 (0.90 to 1.29) | – | ± | ± | Weak evidence of positive association | |
| (5) Heavy lifting or ≥10 kg, ≥10x/day or often | 1.24 (1.07 to 1.43) | + | + | + | Good evidence of positive association | |
| SGA | (1) Lifting <12 kg | 0.97 (0.81 to 1.15) | – | ± | + | Weak evidence of no association |
| (2) Lifting unspecified weight or ≥5 kg | 0.91 (0.47 to 1.76) | – | ± | – | Inconclusive data | |
| (3) Heavy lifting or ≥10 kg, ≤10x/day or rarely | 0.99 (0.91 to 1.08) | ± | – | + | Weak evidence of no association | |
| (4) Heavy lifting or ≥10 kg, unspecified frequency or ≥1x/day | 1.03 (0.71 to 1.51) | – | – | + | Inconclusive data | |
| (5) Heavy lifting or ≥10 kg, ≥10x/day or often | 1.03 (0.87 to 1.21) | – | ± | + | Weak evidence of no association |
*In the case of positive association (summary RE ≥1.05), statistical precision is based on the lower limit of 95% CI with the following interpretation: >1.00: good; 0.91–1.00: moderate; ≤0.90: low. In the case of no association (summary RE <1.05), statistical precision is based on the upper limit of 95% CI with the following interpretation: <1.05: good; 1.05–1.14: moderate; ≥1.15: low.
†Assessment of sensitivity analyses is based on the number of results similar to the summary RE with the following interpretation: 6: good; 3–5: moderate; 0–2: low.
‡Consistency is considered good when I2 <30% and p-value ≥0.10, moderate when (30% ≤I2 ≤50%) and p-value ≥0.10, and low when I2 >50% or p-value <0.10.
§The strength of evidence is attributed as follows: good if the assessment of the three aspects is good; moderate if the assessment of two aspects is good but moderate for the third; weak if the assessment of one aspect is low; inconclusive if the assessment of more than one aspect is low.
+, good; -, low; ±, moderate; PTD, preterm delivery; SA, spontaneous abortion; SGA, small-for-gestational-age; SRE, summary risk estimate.