Pooled OR (95% CI), heterogeneity (I2 and p value of the outcomes)
| Cohort studies | |||||
| Outcome | Reference of studies included | Total number of studies included | Pooled OR (95% CI) | I2 (%) | P value |
| Mortality (unadjusted) | 11–13 16 36 38 43 48 51 55 59 63 64 66 68 | 15 | 3.25 (2.10 to 5.03) | 70 | <0.00001 |
| Mortality (adjusted) | 5 7 12 36 38 66 | 6 | 2.37 (1.40 to 4.01) | 36 | 0.001 |
| Any-grade IVH (unadjusted) | 7 11 13 16 46 48 51 55 60 68 | 10 | 2.30 (1.55 to 3.40) | 36 | <0.00001 |
| Any-grade IVH (adjusted) | 7 38 | 2 | 2.60 (1.09 to 6.20) | 0 | 0.03 |
| Severe IVH (unadjusted) | 5 13 16 43 59 63 64 66 68 | 9 | 1.85 (1.37 to 2.51) | 39 | <0.00001 |
| Severe IVH (adjusted) | 66 | 1 | 0.80 (0.20 to 3.20) | NA | 0.75 |
| Any-stage ROP (unadjusted) | 13 38 40 48 55 59 68 | 7 | 1.78 (1.12 to 2.83) | 42 | 0.01 |
| Any-stage ROP (adjusted) | 38 40 | 2 | 3.70 (1.55 to 8.84) | 0 | 0.003 |
| Severe ROP (unadjusted) | 13 16 40 42 59 60 63 66 68 | 9 | 3.42 (1.82 to 6.41) | 64 | 0.0001 |
| Severe ROP (adjusted) | 8 66 68 | 3 | 1.97 (0.56 to 6.93) | 91 | 0.29 |
| LOS (unadjusted) | 11 13 16 36 43 48 59 63 64 | 9 | 1.97 (1.18 to 3.28) | 69 | 0.009 |
| LOS (adjusted) | 36 53 59 | 3 | 1.38 (0.41 to 4.72) | 81 | 0.60 |
| Undefined NEC (unadjusted) | 5 11 16 46 | 4 | 1.29 (0.72 to 2.30) | 0 | 0.39 |
| Undefined NEC (adjusted) | No study has reported | ||||
| Severe NEC (unadjusted) | 13 36 59 63 64 66 | 6 | 1.91 (0.74 to 4.89) | 47 | 0.18 |
| Severe NEC (adjusted) | 36 59 66 | 3 | 1.78 (0.29 to 10.7) | 65 | 0.53 |
| CLD (unadjusted) | 13 46 55 59 63 64 66 68 | 8 | 2.55 (1.96 to 3.30) | 0 | <0.00001 |
| CLD (adjusted) | 38 59 66 | 3 | 1.42 (0.85 to 2.37) | 0 | 0.18 |
| PVL (unadjusted) | 13 63 64 66 | 4 | 1.01 (0.40 to 2.56) | 0 | 0.98 |
| PVL (adjusted) | 66 | 1 | 0.50 (0.20 to 1.25 | NA | 0.14 |
| Any disability (unadjusted) | 63 64 66 | 3 | 2.35 (1.47 to 3.73) | 0 | 0.003 |
| Any disability (adjusted) | 63 | 1 | 1.27 (0.56 to 2.86) | NA | 0.57 |
| Case–control studies | |||||
| Mortality (unadjusted) | 14 | 1 | 3.24 (0.72 to 14.44) | NA | 0.12 |
| Mortality (adjusted) | No studies available | ||||
| Any-grade IVH (unadjusted) | 15 | 1 | 2.3 (1.3 to 4.07) | NA | 0.004 |
| Any-grade IVH (adjusted) | No studies available | ||||
| Severe IVH (unadjusted) | 14 15 | 2 | 2.58 (1.48 to 4.48) | 0 | 0.0008 |
| Severe IVH (adjusted) | 14 | 1 | 10.33 (10 to 10.67) | NA | <0.00001 |
| Any-stage ROP (unadjusted) | 37 44 69 | 3 | 6.49 (1.97 to 2139) | 82 | 0.002 |
| Any-stage ROP (adjusted) | 37 44 54 | 3 | 1.26 (0.79 to 2.00) | 52 | 0.33 |
| Severe ROP (unadjusted) | 45 50 65 | 3 | 2.15 (1.98 to 2.34) | 0 | <0.00001 |
| Severe ROP (adjusted) | 45 50 54 61 | 4 | 1.01 (0.96 to 1.07) | 42 | 0.67 |
| LOS (unadjusted) | No studies available | ||||
| LOS (adjusted) | No studies available | ||||
| Undefined NEC (unadjusted) | No studies available | ||||
| Undefined NEC (adjusted) | No studies available | ||||
| Severe NEC (unadjusted) | No studies available | ||||
| Severe NEC (adjusted) | No studies available | ||||
| CLD (unadjusted) | 14 | 1 | 3.07 (0.87 to 10.81) | NA | 0.08 |
| CLD (adjusted) | No studies available | ||||
| PVL (unadjusted) | No studies available | ||||
| PVL (adjusted) | No studies available | ||||
| Any disability (unadjusted) | No studies available | ||||
| Any disability (adjusted) | No studies available | ||||
CLD, chronic lung disease; IVH, intraventricular haemorrhage; LOS, late-onset sepsis; NA, not applicable; NEC, necrotising enterocolitis; PVL, periventricular leucomalacia; ROP, retinopathy of prematurity.