Long-chain polyunsaturated fatty acids (LCPUFAs), arachidonic acid (AA omega-6; 20:4ω-6), and docosahexaenoic acid (DHA omega-3; 22:6ω-3), are required for the formation of non-myelinated cell membranes in the central nervous system, including in the retina, hence the great importance of them for appropriate visual and cognitive development.

In this study, the investigators assessed anthropometric, visual, auditory, and psychomotor development in very preterm infants who had diets supplemented with different LCPUFA amount of AA to support the importance of sufficient AA values in formula.

the investigators carried out a prospective randomized controlled double blinded trial in order to study nutritional supplements for preterm infants <1500 grams and/or <32 weeks gestational age (GA) who were born in clinical University Hospital of Santiago de Compostela (CHUS). They were enrolled for a period of 14 months (from July 2011 to August 2012) and followed up from birth until 2 years of age. Milk formulas were provided either as adjunct to insufficient amount of breast milk, or as full formula feeding. Breastfeeding was actively encouraged. Patients were randomized into one of the two formula groups, depending on the type of formula they were to receive. Group A's formula was supplemented with DHA (0.3% of all fatty acids) and AA (0.6%) with an ω-6/ω-3 ratio of 2/1. Group B's formula was supplemented with DHA (0.3%) and AA (0.3%) with an ω-6/ω-3 ratio of 1/1.

Primary outcome:

Assessment of psychomotor development with the Brunet Lézine scale at 2 years of age (Early Care Unit CHUS)

Secondary outcomes:

Physical examination and anthropometric measurements (weight, length, and head circumference) at birth and at 3, 6, 9, 12, 18, and 24 months of age (Neonatology Unit CHUS) Blood levels of fatty acids in the first week of life and at 3 months, 6 months, and 12 months. (Metabolic Unit. Hospital de Cruces, Bilbao) Visual- and auditory-evoked potentials at 6 and 12 months of age (Neurophysiology Unit CHUS)

Inclusion Criteria:

• Living infants who were less than 1500 grams and/or less than 32 weeks gestational age, and whose parents accepted and subscribed the informed consent

Exclusion Criteria:

• Preterm infants with any severe malformation.
• Extremely preterm infants with a gestational age of less than 25 weeks.
• Infants whose parents could not complete the follow-up process in our study center.
• Preterm infants with severe intraventricular hemorrhage or periventricular leukomalacia (more than grade 2).
• Neonates who did not need supplementary milk nutrition, i.e. breastfed-only children.