| Reference | Study type | Population | Intervention and comparison | Outcomes | Risk of bias |
|---|---|---|---|---|---|
| RCT=randomized controlled trial; SR=systematic review; MA=meta-analysis | |||||
| «Tamblyn JA, Pilarski NSP, Markland AD, ym. Vitamin...»1 | SR/MA of observational studies. | Women with miscarriage or recurrent miscarriage was initially confined to preconception
or the first or shortly after the first trimester. Vitamin D serum assessment using the 25(OH)D levels. Europe, North America |
Vitamin D treatment compared to no vitamin D treatment or routine supplementation (400IU). The association between different levels of serum 25(OH)D and the risk of miscarriage or recurrent miscarriage | Primary: miscarriage or recurrent miscarriage | High |
| «Zhang H, Huang Z, Xiao L, ym. Meta-analysis of the...»2 | MA of observational studies | Case–control and cohort studies with pregnant women. Europe, Australia, Asia, United States. |
The association of serum 25-hydroxyvitamin D (25(OH)D) and spontaneous pregnancy loss. | Primary: spontaneous pregnancy loss rate | High |
| Reference | Comments |
|---|---|
| «Tamblyn JA, Pilarski NSP, Markland AD, ym. Vitamin...»1 | Most of the studies included did not originally set out to examine the effect of vitamin supplementation on the risk of miscarriage. Highly heterogeneous evidence was identified. Unknown number of first trimester losses did not include. Included studies could have been influenced by the different methods to quantify the serum 25(OH)D concentration. |
| «Zhang H, Huang Z, Xiao L, ym. Meta-analysis of the...»2 | Methodological diversity would indicate the studies have different degrees of bias. Included studies could have been influenced by the different methods to quantify the serum 25(OH)D concentration. |
Results
| Reference | Intervention and comparison/outcome | Number of studies and number of patients (I/C) | Absolute number of events (%) I | Absolute number of events (%) C | Relative effect (95% CI) |
|---|---|---|---|---|---|
| Level of evidence: very low. The level of evidence is downgraded due to study limitations and imprecision. |
|||||
| «Tamblyn JA, Pilarski NSP, Markland AD, ym. Vitamin...»1 | Vitamin D deficient (<50 nmol/l) versus sufficient (>75 nmol/L) | 4 (1968/1706) | 92 (4,7) | 49 (2,9) | OR 1,94 (1,25-3,02) |
| «Tamblyn JA, Pilarski NSP, Markland AD, ym. Vitamin...»1 | Vitamin D deficient+ insufficient (<75 nmol/L) versus sufficient (>75 nmol/L) | 6 (4102/2236) | 209 (5,1) | 88 (3,9) | OR 1,6 (1,11–2,3) |
| «Zhang H, Huang Z, Xiao L, ym. Meta-analysis of the...»2 | Vitamin D <75 nmol/L versus ≥75 nmol/L | 5 (5518/2068) | 127 (2,3) | 30 (1,5) | RR 1,56 (0,92-2,56) |
| «Zhang H, Huang Z, Xiao L, ym. Meta-analysis of the...»2 | Vitamin D <50 nmol/L versus ≥75 nmol/L | 4 (2076/1986) | 48 (2,3) | 30 (1,5) | RR 1,55 (0,71-3,35) |
| «Zhang H, Huang Z, Xiao L, ym. Meta-analysis of the...»2 | Vitamin D <50 nmol/L versus ≥50 nmol/L | 4 (2076/5388) | 48 (2,3) | 101 (1,9) | RR 1,32 (0,94-1,86) |
| «Zhang H, Huang Z, Xiao L, ym. Meta-analysis of the...»2 | Vitamin D <50 nmol/ L versus ≥50 nmol/L in the first trimester | 2 (414/1387) | 14 (3,4) | 28 (2,0) | RR 2,24 (1,15-4,37) |