Summary of studies on normal values in preterm infants
| Reference | No of preterm infants | Mean gestation (completed weeks) | Type of feeds | Ventilated | Nursing position | Reflux index (%) |
| Eweret al 6 | 19 | 32 | Enteral (3–4 hourly) | No | Not stated | 11.91-150 |
| Changet al 7 | 20 | 32 | Enteral (3 hourly) | No | Supine | 2.03 (2.31) |
| Pradeauxet al 8 | 42 | 31 | Parenteral | Yes | Supine | 3.5 (3.3) |
| Newell et al 9 | 35 | 281-151 | Mixed | Mixed | Prone or lateral | 4.5 (1.0) |
| Ng and Quak10 | 21 | 301-152 | Enteral (1–3 hourly) | No | Not stated | 0.7 (1.1) |