Participants receive preterm formula (PTF) as supplemental feeding when the clinician determines maternal milk supply is insufficient.

Randomization 1 will occur when the clinician determines that supplemental feeding is required due to insufficient breast milk supply.

Randomization 2 will be conducted when the total daily intake of human milk (including own mother's milk [OMM] and/or donor pasteurized human milk [pHDM] ) reaches between 60-120 mL/kg

Randomization 2 will be conducted: Add fortifiers when the infant meets predefined criteria for growth faltering (Preterm infants exhibit a sustained decline in growth velocity for weight, length, or head circumference, demonstrated by a downward crossing of centiles on growth curves, despite tolerating and consuming at least 180 mL/kg/day of breast milk or formula. Blood urea levels in these infants remain consistently below 1.5 mmol/L, and there are no severe complications such as active sepsis or the need for vasoactive medications to maintain circulatory stability. Chronic sodium depletion has also been ruled out, as this condition alone can lead to growth failure. Additionally, preterm infants are unable to tolerate high-volume feeding of 180 mL/kg/day due to specific reasons, such as severe gastroesophageal reflux or the presence of a high-output stoma following surgical procedures).

Medically treated NEC: Diagnosis of necrotizing enterocolitis that required medical (non-surgical) treatment, such as bowel rest and antibiotic therapy.

Treated retinopathy of prematurity (ROP): ROP that progressed to a stage requiring medical or surgical intervention, including laser therapy or intravitreal injections.

Hearing impairment: Documented hearing loss identified through newborn hearing screening or diagnostic audiology tests, potentially requiring follow-up or intervention.

Severe brain injury: Presence of significant brain injury such as Grade III or IV intraventricular hemorrhage (IVH) or periventricular leukomalacia (PVL) as diagnosed by cranial imaging.

Length of hospital stay: Total number of days from birth until discharge from the hospital.

Number of episodes of bloodstream infection: Total number of confirmed bloodstream infections (positive blood cultures) during the hospital stay.

Number of days of antibiotic treatment: Cumulative number of days the infant received systemic antibiotic therapy during hospitalization.

Number of days on parenteral nutrition: Total number of days the infant received intravenous nutritional support due to inability to tolerate full enteral feeds.

Number of days of NPO: Total number of days the infant was designated "nil per os" (NPO), meaning no enteral feeding was given.

Growth parameters (weight): Measurements of the infant's body weight at 2 years corrected age.

Body length: Measurements of the infant's body length at 2 years corrected age.

Head circumference: Measurements of the infant's head circumference at 2 years corrected age.

Survival without moderate to severe cognitive or language impairment. PARCA-R stands for Parent Report of Children's Abilities-Revised. It is a parent completed questionnaire that can be used to assess children's cognitive and language development at 24 months of age.