Summary of results for systematic reviews of observational studies
| Review | Number studies/individuals | Effect size (CI) risk ratio, random effects | Heterogeneity (I2) | Significance (p value)* | GRADE |
| Preterm birth | |||||
| Harvey14 | 7/1792 | NR; one individual study showed significance and six others not significant | NR | + (n=1)† − (n=6) | Very low |
| Newberry32 | 2/371 | NR; by individual study | NR | + (n=1)† − (n=1) | Very low |
| Qin25‡‡ | 10/10 098 | 1.19 (1.08 to 1.31) | 28% | + (0.004) | Moderate |
| Wei29 | 4/1111 | 1.27 (1.03 to 1.58) (blood level 25(OH)D<50 nmol/L) | 28% | − (0.03) | Very low |
| 1.05 (0.98 to 1.12) (blood level 25(OH)D<75 nmol/L) | 0% | − (0.17) | Very low | ||
| Zhou26‡ | 16/16 996 |
1.13
(1.04
to
1.23) (<50 vs >50 nmol/L) | 45% | + (0.003) | Moderate |
| 15/17 122 | 1.03 (0.98 to 1.08) (<75 vs >75 nmol/L) | 65% | − (0.29) | Low | |
| Pre-eclampsia | |||||
| Chung13 | 1/1189 | 5 (1.7 to 14.1)§ | NR | + (n=1)† | Very low |
| Harvey14 | 4/642 | 0.75 (0.48 to 1.19)§ | 80.8% | − (0.001) | Very low |
| Newberry32 | 8/4420 | NR; by individual study | NR | + (n=5) − (n=3) | Very low |
| Tabesh30 | 8/2485 | 2.02 (1.26 to 3.23) | 53% | + (0.04) | Very low |
| Wei29 ‡ | 6/2008 |
1.57
(1.21
to
2.03) (<50 nmol/L) | 39% | + (0.0006) | Low |
| 5/1311 | 1.21 (0.99 to 1.46) (<75 nmol/L) | 60% | − (0.06) | Very low | |
| Gestational diabetes | |||||
| Harvey14 | 8/2668 | NR; by individual study | NR | + (n=3) † − (n=5) | Very low |
| Lu15 | 20/16 515 | 1.45 (1.15 to 1.83)§ | 66.6% | + (0.002) | Low |
| Wei29‡ | 10/4126 |
1.12
(1.02
to
1.22) (<50 nmol/L) | 27% | + (0.02) | Moderate |
| 8/3840 |
1.09
(1.03
to
1.15) (<75 nmol/L) | 28% | + (0.002) | Moderate | |
| Small for gestational age | |||||
| Harvey14 | 7/5660 | NR; by individual study | NR | + (n=2) † − (n=5) | Very low |
| Newberry32 | 1/412 | NR; by individual study | NR | NR | Very low |
| Wei29 ‡ | 6/6013 |
1.35
(1.18
to
1.54) (<50 nmol/L) | 15% | + (0.00001) | Low |
| 5/2283 | 0.99 (0.83 to 1.18) (<75 nmol/L) | 75% | − (0.92) | Very low | |
| Low birth weight | |||||
| Harvey14 | 3/1676 | NR; by individual study | NR | + (n=1)† − (n=2) | Very low |
| Caesarean section | |||||
| Harvey14 | 6/3277 | NR; by individual study | NR | + (n=2) † − (n=4) | Very low |
*Significance indicated as positive (+) when p value≤0.05 and negative (−) if >0.05.
†In absence of pooled data, this indicates the number of studies with positive or negative statistical significance.
‡For each outcome, the review with the highest level of evidence is presented in bold font.
§Reported as odds ratios as insufficient data available to convert to risk ratio.
25 (OH)D, 25-hydroxy vitamin D.