Summary of findings 2. A dose of vitamin D 4000 IU/d or more compared to 3999 IU/d or less alone or with any other nutrient for women during pregnancy.
| A dose of vitamin D 4,000 IU/d or more compared to 3999 IU/d or less alone or with any other nutrient for women during pregnancy | ||||||
| Patient or population: women during pregnancy Setting: trials were carried out between 2004 to 2017 in the following countries: Australia (Yap 2014), Bangladesh (Bacqui 2009; Roth 2013), Iran (Hashemipour 2014; Karamali 2015; Mojibian 2015; Rostami 2017), and the USA (Stephensen 2011; Wagner 2006a; Weiss 2009). Most trials were conducted outside the tropics and in different seasons. Intervention: a dose of vitamin D 4,000 IU/d or more Comparison: 3999 IU/d or less alone or with any other nutrient | ||||||
| Outcomes | Anticipated absolute effects* (95% CI) | Relative effect (95% CI) | № of participants (studies) | Certainty of the evidence (GRADE) | Comments | |
| Risk with 3999 IU/d or less alone or with any other nutrient | Risk with A dose of vitamin D 4000 IU/d or more | |||||
| Pre‐eclampsia | Study population | RR 0.87 (0.62 to 1.22) | 1903 (4 RCTs) | ⊕⊕⊝⊝ LOW 1 | Included trials: Karamali 2015; Rostami 2017; Weiss 2009; Yap 2014 | |
| 81 per 1000 | 71 per 1000 (50 to 99) | |||||
| Gestational diabetes | Study population | RR 0.89 (0.56 to 1.42) | 2276 (5 RCTs) | ⊕⊕⊝⊝ LOW 1 | Included trials: Hashemipour 2014; Roth 2013; Wagner 2006a; Yap 2014 | |
| 29 per 1000 | 26 per 1000 (16 to 41) | |||||
| Preterm birth | Study population | RR 0.85 (0.64 to 1.12) | 2948 (6 RCTs) | ⊕⊕⊝⊝ LOW 2 | Included trials: Bacqui 2009; Karamali 2015; Rostami 2017; Roth 2013; Wagner 2006a; Weiss 2009 | |
| 75 per 1000 | 64 per 1000 (48 to 84) | |||||
| Low birthweight | Study population | RR 0.92 (0.49 to 1.70) | 1099 (2 RCTs) | ⊕⊕⊝⊝ LOW 3 | Included trials: Karamali 2015; Roth 2013 | |
| 177 per 1000 | 163 per 1000 (87 to 300) | |||||
| *The risk in the intervention group (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; OR: Odds ratio; | ||||||
| GRADE Working Group grades of evidence High certainty: We are very confident that the true effect lies close to that of the estimate of the effect Moderate certainty: We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different Low certainty: Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect Very low certainty: We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect | ||||||
1 We downgraded (2) levels for serious limitations in study design due to one trial being assessed as high risk of bias for one domain and one study being at unclear risk for allocation concealment and for serious limitations in imprecision with wide confidence intervals crossing the line of no effect.
2 We downgraded (2) levels for serious limitations in study design due to one trial being assessed as high risk of bias for several domains and for serious limitations in imprecision with wide confidence intervals crossing the line of no effect.
3 We downgraded (2) levels for very serious limitations in imprecision as only two trials contributed data to this outcome, with wide confidence intervals crossing the line of no effect and for serious limitations in indirectness as both studies were conducted in Asian women.