Unlabelled: To assess the association between postnatal growth and neurodevelopment at the age of 2 years in extremely low gestational age newborns (ELGAN, < 28 weeks' gestation). Retrospective population-based cohort study including all live born ELGAN in 2006-2012 in Switzerland. Growth parameters (weight, length, head circumference, body mass index) were assessed at birth, at hospital discharge home, and 2-year follow-up (FU2). Unadjusted and adjusted regression models assessed associations between growth (birth to hospital discharge and birth to FU2) and neurodevelopment at FU2. A total of 1244 infants (mean GA 26.5 ± 1.0 weeks, birth weight 853 ± 189 g) survived to hospital discharge and were included in the analyses. FU2 was documented for 1049 (84.3%) infants. The mean (± SD) mental and a psychomotor development index at 2FU were 88.9 (± 18.0) and 86.9 (± 17.7), respectively. Moderate or severe neurodevelopmental impairment was documented in 23.2% of patients. Changes of z-scores between birth and discharge and between birth and FU2 for weight were - 1.06 (± 0.85) and - 0.140 (± 1.15), for length - 1.36 (± 1.34), and - 0.40 (± 1.33), for head circumference - 0.61 (± 1.04) and - 0.76 (± 1.32) as well as for BMI 0.22 (± 3.36) and - 0.006 (± 1.45). Unadjusted and adjusted analyses showed that none of the four growth parameters was significantly associated with any of the three outcome parameters of neurodevelopment. This was consistent for both time intervals.

Conclusion: In the present population-based cohort of ELGAN, neither growth between birth and hospital discharge nor between birth and FU2 were significantly associated with neurodevelopment at age of 2 years.

What is known: • Studies assessing the association between growth and neurodevelopment in extremely low gestational age newborns (28 weeks' gestation) show conflicting results.

What is new: • Neither growth between birth and hospital discharge nor between birth and corrected age of 2 years were significantly associated with neurodevelopment at age of 2 years. • The role of postnatal growth as a predictor of neurodevelopmental outcome during infancy might be smaller than previously assumed.