Comparison 1. Human milk‐derived vs. Bovine milk‐derived fortifier.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Necrotizing Enterocolitis Stage 2 or greater	1	125	Risk Ratio (M‐H, Fixed, 95% CI)	0.95 [0.20, 4.54]
2 Death	1	125	Risk Ratio (M‐H, Fixed, 95% CI)	0.71 [0.17, 3.06]
3 Weight: Change during intervention (g)	1	118	Mean Difference (IV, Fixed, 95% CI)	‐179.0 [‐386.38, 28.38]
4 Weight‐for‐age z score (change during intervention)	1	118	Mean Difference (IV, Fixed, 95% CI)	‐0.2 [‐0.73, 0.33]
5 Length: Change during intervention (cm)	1	118	Mean Difference (IV, Fixed, 95% CI)	‐0.80 [‐2.25, 0.65]
6 Length‐for‐age z score (change during intervention)	1	118	Mean Difference (IV, Fixed, 95% CI)	0.10 [‐0.57, 0.77]
7 Head circumference: Change during intervention (cm)	1	118	Mean Difference (IV, Fixed, 95% CI)	‐0.60 [‐1.52, 0.32]
8 Head circumference‐for‐age Z score (change during intervention)	1	118	Mean Difference (IV, Fixed, 95% CI)	0.0 [‐0.49, 0.49]
9 Feeding interruption requiring parenteral nutrition	1	125	Risk Ratio (M‐H, Fixed, 95% CI)	2.86 [0.31, 26.75]
10 Gastric residuals	1	125	Risk Ratio (M‐H, Fixed, 95% CI)	0.99 [0.65, 1.51]
11 Abdominal distension	1	125	Risk Ratio (M‐H, Fixed, 95% CI)	0.93 [0.80, 1.10]
12 Late‐onset sepsis	1	125	Risk Ratio (M‐H, Fixed, 95% CI)	0.54 [0.25, 1.21]
13 Bronchopulmonary dysplasia	1	125	Risk Ratio (M‐H, Fixed, 95% CI)	0.85 [0.48, 1.51]
14 Retinopathy of prematurity requiring intervention	1	121	Risk Ratio (M‐H, Fixed, 95% CI)	0.16 [0.02, 1.28]
15 Necrotizing Enterocolitis Stage 2 or greater	1	125	Risk Difference (M‐H, Fixed, 95% CI)	‐0.00 [‐0.08, 0.07]
16 Feeding interruption requiring parenteral nutrition	1	125	Risk Difference (M‐H, Fixed, 95% CI)	‐0.02 [‐0.10, 0.06]
17 Gastric residuals	1	125	Risk Difference (M‐H, Fixed, 95% CI)	‐0.00 [‐0.18, 0.17]
18 Abdominal distension	1	125	Risk Difference (M‐H, Fixed, 95% CI)	‐0.06 [‐0.19, 0.08]
19 Death	1	125	Risk Difference (M‐H, Fixed, 95% CI)	‐0.02 [‐0.10, 0.06]
20 Late‐onset sepsis	1	125	Risk Difference (M‐H, Fixed, 95% CI)	‐0.10 [‐0.24, 0.03]
21 Bronchopulmonary dysplasia	1	125	Risk Difference (M‐H, Fixed, 95% CI)	‐0.05 [‐0.20, 0.11]
22 Retinopathy of prematurity requiring intervention	1	121	Risk Difference (M‐H, Fixed, 95% CI)	‐0.09 [‐0.17, ‐0.00]