This study will be comparing the postnatal growth of moderate to late preterm infants in the Neonatal Intensive Care Unit (NICU) born between gestational ages of 30 weeks 0 days to 35 weeks and 6 days who are receiving enteral feeds of mother's own breast milk using the NICU's standard nutritional fortification protocol versus a targeted nutritional fortification protocol.

Infants in the NICU born between gestational ages 30 weeks 0 days and 35 weeks 6 days will be screened to determine if they are receiving unfortified mother's breast milk for enteral nutrition. Informed consent will be obtained from these lactating mothers for themselves and their infants to participate in the study. Once enrolled in the study, the mother and infant dyad will be randomized using an electronic tool for block randomization into standard fortification arm (control group) or targeted fortification arm (intervention group). Maximum of 100 infants will be assigned to each arm to ensure statistical significance. The physician team, study statisticians, and the mothers will be blinded in their group assignment.

Mothers will be provided with one-on-one teaching (with verbal and written instructions) by the NICU certified lactation consultants or by an authorized, trained study personnel on how to pool their pumped breast milk for 24 hours, referenced as "breast milk pooling." They will also be shown how to prepare a 10 mL sample of the pooled breast milk for analysis. Pooled breast milk will be analyzed for macronutrient content (protein, carbohydrate, fat, and calories) using Miris Human Milk Analyzer before fortification once a week for both arms of the study. All infants in both groups will follow the enteral feeding advancement schedule until the infant is ready for nutritional fortification.

In the standard fortification arm (control group), mother's breast milk will be fortified using Enfamil Liquid Human Milk Fortifier (LHMF) as per standard feeding protocol defined by Loma Linda University Children's Hospital Neonatal Intensive Care Unit. The feeding protocol, specific to birth weight, is available online in the LLUCH NICU Manual.

In the targeted fortification arm (intervention group), mother's breast milk will be fortified in modular fashion. For protein supplementation, Amino Acid powder will be utilized as a modular component. For carbohydrate supplementation, PolyCal will be utilized. For lipid supplementation, safflower oil will be utilized. Fortification goals for this group will follow the macronutrient intake recommendations for preterm infants published by the European Society of Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) Committee on Nutrition in 2009. The goal energy level will be between 110 - 135 kcal/kg/day, goal protein level between 3.5 - 4.5 g/kg/day, goal lipid level between 4.8 - 6.6 g/kg/day, and goal carbohydrate level between 11.6 - 13.2 g/kg/day. The goal total daily fluid volume will be between 150 to 180 mL/kg/day.

NICU Registered Dietitians will be provided with the macronutrient contents of pooled breast milk from mothers of babies in the intervention group. Using the aforementioned values from ESPGHAN guideline for each macronutrient, they will provide recommendations on specific amounts of modular supplementation to be added to the pooled breast milk. Based on these recommendations, all un-pooled expressed breast milk of mothers in the intervention group will be fortified in a customized manner by the milk technicians in the NICU milk room and given to infants in the intervention group. NICU Registered Dieticians will not be provided with analysis results showing macronutrient levels of the pooled milk or standard fortified milk in the control group as the current standard of care at LLUCH NICU does not include macronutrient analysis of pooled breast milk for babies born >30 weeks gestation.

Infants enrolled in both arms will have their anthropometric measurements taken once a week from birth to NICU discharge. Anthropometric measurements will include weight, height, and head circumference. The Z-scores of weight, height, and head circumference will be recorded and analyzed for any statistical differences.

Inclusion Criteria:

• Singleton preterm infants
• Between 30 weeks 0 days and 35 weeks and 6 days
• Receiving any amount of mother's breast milk as a form of enteral nutrition
• Mother is ≥ 18 y/o

Exclusion Criteria:

• Not receiving any breast milk
• Congenital anomalies or surgical conditions that interfere with enteral feeding

Mother, physician team, and study statistician will be blinded to randomization.