ABSTRACT: BACKGROUND:Preterm infants born 30 to 33?weeks' gestation often require early support with intravenous fluids because of respiratory distress, hypoglycemia or feed intolerance. When full feeds are anticipated to be reached within the first week, risks associated with intravenous delivery mode and type must be carefully considered. Recommendations are for parenteral nutrition to be infused via central venous lines (because of the high osmolarity), however, given the risks associated with central lines, clinicians may opt for 10% glucose via peripheral venous catheter when the need is short-term. We therefore compare a low osmolarity peripheral intravenous parenteral nutrition (P-PN) solution with peripheral intravenous 10% glucose on growth rate in preterm infants born 30 to 33?weeks' gestation. METHODS:In this parallel group, single centre, superiority, non-blinded, randomised controlled trial, 92 (P-PN 42, control 50) infants born 30+?0 to 33+?6 weeks' gestation, were randomised within 24?h of age, to receive either P-PN (8% glucose, 30?g/L amino acids, 500?IU/L heparin and SMOFlipid®) or a control of peripheral intravenous 10% glucose. Both groups received enteral feeds according to hospital protocol. The primary outcome was rate of weight gain from birth to 21?days of age. RESULTS:The rate of weight gain was significantly increased in P-PN infants compared with control (P-PN, n?=?42, 18.7, SD 6.6?g/d vs control, n?=?50, 14.8, SD 6.0?g/d; adjusted mean difference 3.9?g/d, 95% CI 1.3 to 6.6; P?=?0.004), with the effect maintained to discharge home. Days to regain birthweight were significantly reduced and length gain significantly increased in P-PN infants. One infant in the P-PN group had a stage 3 extravasation which rapidly resolved. Blood urea nitrogen and triglyceride levels were significantly higher in the P-PN group in the first week of life, but there were no instances of abnormally high levels. There were no significant differences in any other clinical or biochemical outcomes. CONCLUSION:P-PN improves the rate of weight gain to discharge home in preterm infants born 30 to 33?weeks gestation compared with peripheral intravenous 10% glucose. TRIAL REGISTRATION:Australian New Zealand Clinical Trials Registry ACTRN12616000925448 . Registered 12 July 2016.