OBJECTIVE: To investigate in extremely low birthweight (ELBW
<
1000 g) babies the associations between refeeding syndrome (serum phosphate <
1.4 mmol·L DESIGN: Secondary cohort analysis of the ProVIDe trial participants with serum biochemistry within 7 days of birth. At 2 years' CA, neurodisability was assessed by Bayley Scales of Infant Development Edition III and neurological examination. Associations between neurodisability and other variables were analysed using t-tests and logistic regression adjusted for sex and smallness-for-gestational age. SETTING: Six tertiary neonatal intensive care units (NICUs) in New Zealand. PARTICIPANTS: 352 ELBW babies born between 29 April 2014 and 30 October 2018. MAIN OUTCOME MEASURE: Death or neurodisability at 2 years' CA. RESULTS: Fifty-nine babies died, two after discharge from the NICU. Of the 336 babies who survived to 2 years' CA, 277 had neurodevelopmental assessment and 107 (39%) had a neurodisability. Death or neurodisability was more likely in babies who had refeeding syndrome (aOR 1.96 (95% CI 1.09 to 3.53), p=0.02) and in babies who had hypophosphataemia (aOR 1.74 (95% CI 1.09 to 2.79), p=0.02). Hypophosphataemia was associated with increased risk of death (aOR 2.07 (95% CI 1.09 to 3.95), p=0.03)) and severe hypophosphataemia (<
0.9 mmol·L CONCLUSIONS: In ELBW babies, refeeding syndrome and hypophosphataemia in the first week are associated with death or neurodisability. Until optimal phosphate requirements are determined through further research, monitoring for hypophosphataemia and mitigation strategies are indicated. TRIAL REGISTRATION NUMBER: ACTRN12612002084875.