Summary of findings for the main comparison. Zinc supplementation versus no zinc (with or without placebo) for improving pregnancy and infant outcome.
| Zinc supplementation versus no zinc (with or without placebo) for improving pregnancy and infant outcome | ||||||
| Population: Normal pregnant women with no systemic illness Settings: Bangladesh, Chile, China, Denmark, Egypt, Ghana, Indonesia, Iran, Nepal, Pakistan, Peru, South Africa, UK, USA Intervention: Zinc supplementation versus no zinc (with or without placebo) | ||||||
| Outcomes | Illustrative comparative risks* (95% CI) | Relative effect (95% CI) | No of Participants (studies) | Quality of the evidence (GRADE) | Comments | |
| Assumed risk | Corresponding risk | |||||
| Control | Zinc supplementation versus no zinc (with or without placebo) | |||||
| Preterm birth | Study population | RR 0.86 (0.76 to 0.97) | 7637 (16 studies) | ⊕⊕⊕⊝ moderate1 | ||
| 129 per 1000 | 111 per 1000 (98 to 125) | |||||
| Moderate | ||||||
| 100 per 1000 | 86 per 1000 (76 to 97) | |||||
| Stillbirth or neonatal death | Study population | RR 1.12 (0.86 to 1.46) | 5100 (8 studies) | ⊕⊕⊝⊝ low1,2 | ||
| 40 per 1000 | 45 per 1000 (34 to 58) | |||||
| Moderate | ||||||
| 25 per 1000 | 28 per 1000 (22 to 37) | |||||
| Birthweight | The mean birthweight in the intervention groups was 0.9lower (22.2 lower to 24.0 higher) | 6757 (17 studies) | ⊕⊕⊝⊝ low1,2 | |||
| Small‐for‐gestational age | Study population | RR 1.02 (0.94 to 1.11) | 4252 (8 studies) | ⊕⊕⊕⊝ moderate1 | ||
| 265 per 1000 | 270 per 1000 (249 to 294) | |||||
| Moderate | ||||||
| 108 per 1000 | 110 per 1000 (102 to 120) | |||||
| Low birthweight | Study population | RR 0.93 (0.78 to 1.12) | 5643 (14 studies) | ⊕⊕⊕⊝ moderate1 | ||
| 196 per 1000 | 182 per 1000 (153 to 219) | |||||
| Moderate | ||||||
| 119 per 1000 | 111 per 1000 (93 to 133) | |||||
| *The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval; RR: Risk ratio; | ||||||
| GRADE Working Group grades of evidence High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate. | ||||||
1 Most studies contributing data had design limitations. 2 Wide confidence interval crossing the line of no effect.