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Background & aims: A balanced supply of arachidonic acid (ARA) and docosahexaenoic acid (DHA) may be crucial for quality of growth in preterm infants. This secondary analysis of a randomized controlled trial aimed to determine the effect of enhanced ARA and DHA supplementation on growth and body composition in infants born before 29 weeks of gestation. Furthermore, we aimed to study associations between human milk feeding, growth patterns and body composition.

Methods: The ImNuT-trial randomized 121 infants to receive a daily supplement with medium chain triglycerides (control) or 100 mg/kg ARA and 50 mg/kg DHA (ARA:DHA group) from the second day of life until 36 weeks postmenstrual age. Growth and body composition were evaluated up to 3 months corrected age.

Results: The ARA:DHA group showed better linear growth from birth to term equivalent age compared to the control group; mean difference in z score change from birth for length was 0.74 ([95% CI, 0.17–1.3]; p = 0.010). There were no differences in growth and body composition outcomes at 3 months corrected age between the groups. An increase in z score for weight after 36 weeks postmenstrual age and breastfeeding at 3 months corrected age were the strongest positive predictors of fat mass% at 3 months corrected age (both, p < 0.001).

Conclusion: Early enhanced supplementation of ARA and DHA may be beneficial with respect to somatic growth in very preterm infants.

Clinical trial registration: The trial has been registered on www.clinicaltrials.gov, ID: NCT03555019.