The overall purpose of this project is to identify biomarkers that in combination with clinical variables predict severe complications, such as sepsis, necrotizing enterocolitis (NEC) and neurological impairment, in extremely preterm (EPT) infants (born before gestational week 28+0), so as to customize future treatments for this highly vulnerable patient group. We will perform multi-omic analyses (genome, proteome, metabolome, lipidome, microbiome) in samples from in relation to clinical data in a clinical cohort of EPT infants with help of machine learning technology. The identified biomarkers will subsequently be validated in a second clinical cohort in EPT infants. Specific aims: 1. To reveal possible mechanisms underlying severe complications such sepsis and NEC and neurological impairment in EPT infants by multi-omic analyses. 2. To identify biomarkers that in combination with clinical variables predict severe complications, such as sepsis and NEC and neurological impairment in EPT infants. 3. To identify biomarkers in combination with clinical data can predict in which subgroup of infants, future therapies and diet interventions will reduce severe complications, such as NEC, culture-proven sepsis and neurological impairment. The project is based on the PROPEL and N forte trials which have both ethical approvals (Dnr 2012/28-31 and Dnr 2018/193-31) and have received grants from the Swedish Research Council (Dnr 2014-1846 and Dnr 2020-01111).