Matching Donor Human Milk On Maternal Secretor Status (MMOMSS) Study

Inclusion Criteria: * Gestation up to 33 6/7 weeks at hospital admission (to guarantee at least 14 days intervention, since DHM fortification typically ends at 34+0 weeks adjusted gestational age). * Provision of consent for infant to receive DHM. * Mother has provided signed and dated informed consent and authorization to use protected health information, as required by national and local regulations. * In the investigator's opinion, the subject mother understands and is able to comply with protocol requirements, instructions, and protocol-stated restrictions, and is likely to complete the study as planned. Exclusion Criteria (Infant): * Diagnosed with clinically significant major congenital malformation * Intestinal perforation or stage 2 necrotizing enterocolitis (NEC) * Unlikely to survive the study period * Receiving extended courses of antibiotics (most infants are expected to receive up to 48hr antibiotic prophylaxis at birth according to standard NICU protocol; this criterion will only exclude infants receiving prolonged courses of antibiotics) * Presence prior to enrollment of intestinal perforation or stage 2 necrotizing enterocolitis (NEC) prior to tolerating fortified feeds