Summary of findings for the main comparison. Vitamin D supplementation compared to placebo or no intervention for pregnancy and neonatal health outcomes.
| Vitamin D supplementation compared to placebo/control for pregnancy and neonatal health outcomes | ||||||
| Patient or population: pregnant women and their infants. Setting: trials were carried from 1980s to 2015 in countries from Bangladesh, India, Iran, New Zealand and UK. Most trials were conducted outside the tropics and in different seasons. Intervention: vitamin D supplementation. Comparison: placebo or no intervention. | ||||||
| Outcomes | Anticipated absolute effects* (95% CI) | Relative effect (95% CI) | № of participants (studies) | Certainty of the evidence (GRADE) | Comments | |
| Risk with placebo/control | Risk with vitamin D supplementation | |||||
| Pre‐eclampsia | Study population | RR 0.48 (0.30, 0.79) | 499 (4 RCTs) | ⊕⊕⊕⊝ MODERATE1 | Included trials: Asemi 2013a; Naghshineh 2016; Sablok 2015; Sasan 2017 | |
| 168 per 1000 | 79 per 1000 (49 to 131) | |||||
| Gestational diabetes | Study population | RR 0.51 (0.27 to 0.97) | 446 (4 RCTs) | ⊕⊕⊕⊝ MODERATE 2 | Included trials: Asemi 2013a; Sablok 2015; Shahgheibi 2016; Tehrani 2014 | |
| 127 per 1000 | 65 per 1000 (34 to 123) | |||||
| Maternal adverse events: severe postpartum haemorrhage | Study population | RR 0.68 (0.51 to 0.91) | 1134 (1 RCT) | ⊕⊕⊝⊝ LOW 3 | Included trial: Harvey 2012 | |
| 158 per 1000 | 106 per 1000 (79 to 142) | |||||
| Maternal adverse event: nephritic syndrome | Study population | RR 0.17 (0.01 to 4.06) | 135 (1 RCT) |
⊕⊝⊝⊝ VERY LOW 4,5 | Included trial: Yu 2008 | |
| 22 per 1000 | 4 per 1000 (0 to 90) | |||||
| Maternal adverse event: hypercalcaemia | Study population | Not estimable | 1134 (1 RCT) | ⊕⊕⊝⊝ LOW 3,6 | Included trial: Harvey 2012 | |
| 0 per 1000 | 0 per 1000 | |||||
| Preterm birth (less than 37 weeks' gestation) | Study population | RR 0.66 (0.34 to 1.30) | 1640 (7 RCTs) | ⊕⊕⊝⊝ LOW 7,8 | Included trials: Asemi 2013a; Delvin 1986; Grant 2013; Harvey 2012; Mirghafourvand 2013; Roth 2010; Singh 2015 | |
| 87 per 1000 | 57 per 1000 (29 to 113) | |||||
| Low birthweight (less than 2500 g) | Study population | RR 0.55 (0.35 to 0.87) | 697 (5 RCTs) | ⊕⊕⊕⊝ MODERATE 9 | Included trials: Brooke 1980; Bhutta 2011; Marya 1988; Roth 2010; Sablok 2015 | |
| 136 per 1000 | 75 per 1000 (48 to 118) | |||||
| *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; RCT: randomised controlled trial; RR: Risk 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 (1) level for serious limitations in study design due to one trial being assessed as high risk of bias for several domains and two trials having unclear allocation concealment.
2 We downgraded (1) level for serious limitations in study design due to one trial being assessed as high risk of bias for several domains.
3 We downgraded (2) levels for very serious limitations in study design due to one study being assessed as high risk of other bias because we do not know the impact of the participants who were allowed to continue taking their own multivitamin with 400 IU/d of vitamin D as this was not recorded.
4 We downgraded (1) level for serious limitations in study design due to one study being assessed as high risk of bias for performance and detection bias.
5 We downgraded (2) levels for very serious limitations in imprecision as only one small study, with a small number of events and wide 95% confidence intervals (CI) contributed data.
6 We downgraded (1) level for serious limitations in imprecision due to a single study with zero events contributing data.
7 We downgraded (1) level for serious limitations in study design due to two studies being at unclear risk of selection bias and one study being at high risk of other bias.
8 We downgraded (1) level for serious limitations in imprecision as the 95% confidence interval (CI) was wide and crossed the line of no effect.
9 We downgraded (1) level for serious limitations in study design due to two studies being at unclear risk of selection bias, one study being at high risk of bias for allocation concealment, and three studies being at high risk of attrition bias.