Prematurity is the leading cause for mortality and morbidity in newborns with very low birth weight (VLBW) infants (\< 1500g birth weight) at highest risk. Ten to thirty percent of VLBW infants are also born too small for their gestational age defined by a birth weight below the 10th percentile. In daily neonatal intensive care, consequential long term-follow up and most studies all growth restricted premature infants are treated the same, importantly this includes the nutritional management after birth. However, different groups of patients with different causal pathologies are subsumed under the definition growth restriction or born too small. One group of growth restricted patients refers to the infants born constitutionally small or small for gestational age (SGA). The other group refers to infants with an intrauterine growth restriction (IUGR) caused by a complex antenatal pathology. Consequently, the nutritional management after birth is very important to minimize the potential risk for developing obesity, diabetes and cardiovascular diseases later in life and to achieve optimal growth. So far we do not consider the different underlying pathomechanisms of growth restriction in our nutritional concepts for preterm infants and therefore cause long-term consequences. The European society of pediatric gastroenterology, hematology and nutrition (ESPGHAN) recommends to feed enhanced nutrients up to 52nd week of gestation in all growth restricted preterm infants- regardless if they are SGA or IUGR premature. Actually, reliable data guaranteeing that the recommended "enhanced nutrients strategy" providing extra nutrients up to 52 weeks for SGA and IUGR infants is safe and effective for both groups in terms of long-term growth and metabolic programming are lacking.
A total of 348 preterm infants born and discharged below the 10th percentile at term will be included in the study and stratified according to SGA or IUGR by a combination of antenatal ultrasound parameters and growth parameters (including 10% screening failures and 20% drop out. Furthermore IUGR and SGA growth restricted preterm infants will be stratified according to breastfeeding or formula feeding and randomized in one of the following groups: Standard nutrients group (breastfeeding or starter formula) or Enhanced nutrients group (fortified breast milk or post-discharge formula. Body composition measurements will be performed by air displacement plethysmography - a non-invasive method. Anthropometric measurements will be performed by measuring weight, height and head circumference. Furthermore, parameters of metabolic programming, metabolomics, the stool microbiome and neurodevelopmental outcome will be determined. Additionally, the stool microbiome will be characterized from infant stool samples and compared between the two groups. After an interventional period of three months infants will be followed up until 2 years of age.
