Univariate analysis at the age of 6 weeks
| Normal iron status (n = 65) | Iron deficiency (n = 34) | p-value | |
| Gestational age (in weeks) | 34,0 (SD 0,8) | 33,7 (SD 0,8) | 0.055 |
| Birth weight (in grams) | 2137 (SD 335) | 1757 (SD 379) | 0.000* |
| Mean total fluid (ml/kg per day) | 159,2 (SD 6,2) | 161,2 (SD 4,8) | 0.213 |
| Parenteral feeding (yes) | 4/32 (12,5%) | 19/26 (73,1%) | 0.000* |
| Type of enteral feeding | 0.453 | ||
| - Breast milk | 7/44 (15,9%) | 4/34 (11,8%) | |
| - Formula feeding | 12/44 (27,3%) | 6/34 (17,6%) | |
| - Combination of breast milk and formula feeding | 25/44 (56,8%) | 24/34 (70,6%) | |
| Mean iron intake (in mg/kg per day) | 1,2 (SD 0,8) | 1,0 (SD 0,9) | 0.636 |
| Blood transfusion (yes) | 1/65 (1,5%) | 2/34 (5,9%) | 0.411 |
| Oral iron supplementation (yes) | 0/31 (0%) | 4/26 (15,4%) | 0.024* |
| Blood draws (total number of draws of > 0.2 ml) | 15 (SD 5) | 19 (SD 8) | 0.018* |
| Necrotizing enterocolitis (yes, only Bell stage 1 or 2) | 1/31 (3,2%) | 2/26 (7,7%) | 0.452 |
| Sepsis (yes) | 5/31(16,1%) | 6/26 (23,1%) | 0.508 |
| Infant respiratory distress syndrome (yes) | 1/31 (3,2%) | 3/26 (11,5%) | 0.221 |
| Ferritin at 1 week (in µg/l) | 217 (SD 133) | 132 (SD 89) | 0.004* |
Abbreviations: SD = standard deviation