Background Extremely preterm infants often experience growth failure and adequate nutritional supply may be difficult to achieve. It is still debated to what extent nutrition affects growth at an early stage in life. The aim of this study was to explore associations between energy and macronutrient intakes and growth.

Methods The study population consists of extremely preterm infants born in Sweden during 2004–2007. Detailed data of nutritional intakes and anthropometric measurements were retrieved from hospital records.

Results Infants (n=602) had a mean±SD gestational age of 25.3±1.1 weeks and birth weight 765±171g. From birth to 70 days of age, energy and protein intakes were 119.3±11.3kcal/kg/day and 3.2±0.4g/kg/day respectively. Infants showed postnatal growth failure: mean standard deviation scores (SDS) decreased by 1.5 for weight, 2.3 for length and 0.8 for head circumference.

The following confounders were included in the multivariate analyses: Gestational age, CRIB-score, duration of mechanical ventilation, days on postnatal steroid and antibiotics treatment, infant sex and baseline anthropometrics. Energy intake was significantly correlated with weight gain (r=+0.31, p<0.001), length gain (r=+0.20, p<0.001) and head circumference growth (r=+0.26, p<0.001). In addition, protein intake was independently positively associated with weight gain, and the effect of macronutrient intakes on growth varied with postnatal age.

Conclusions Extremely preterm infants in Sweden received lower macronutrient intakes than recommended and showed postnatal growth failure. We found significant positive correlations between intakes of energy and macronutrients and growth. This suggests that optimized energy and macronutrient intake is important to prevent growth failure in these vulnerable infants.