Exclusive Human-milk in Preterm NEOnates and Early VASCular Aging Risk Factors (NEOVASC)

Preterm-born group: Inclusion Criteria: 1. Extremely preterm infants with a birth weight of 500-1250g. 2. Feeding is NPO or exclusive human milk prior to enrollment. 3. Parent(s) willing to sign informed consent.- Exclusion Criteria: 1. Infants with a birth weight \<500g or \>1250g 2. Subjects diagnosed with inborn errors of metabolism such as galactosemia, phenylketonuria 3. Subjects who have not been NPO or fed exclusive human milk diet prior to enrollment. 4. Presence of major congenital malformation. 5. Presence of intestinal perforation or Stage 2 Necrotizing enterocolitis prior to enrollment. 6. Parent(s) not willing to sign informed consent. 7. Unable to participate for any reason based on the decision of the study investigator (e.g. unlikely to survive the study period). Term-born group: Inclusion criteria 1. Term-born children with an adequate birth weight 2. Parent(s) willing to sign informed consent Exclusion criteria 1. Subjects with acute or chronic illness 2. Parent(s) not willing to sign informed consent