9.2 Nutritional Fortification & Specialized Formula Selection

9.2 Nutritional Fortification & Specialized Formula Selection

The primary nutritional goal for preterm infants is to achieve postnatal growth rates and body composition accretion that approximate normal intrauterine fetal growth (approximately 15 to 20 g/kg/day). Preterm infants miss the critical third-trimester period of rapid nutrient transfer across the placenta, leaving them with negligible nutrient reserves, high metabolic demands, and an immature gastrointestinal tract.

1. Preterm Nutritional Requirements & Fetal Accretion Physiology

During the third trimester of pregnancy (24 to 40 weeks gestation), the fetus undergoes exponential accretion of protein, minerals, and energy stores. When delivery occurs prematurely, enteral nutrient delivery must be precisely formulated to replicate these intrauterine accretion rates.

Daily Preterm Enteral Nutritional Targets (AAP & ESPGHAN Guidelines)

2. Limitations of Unfortified Human Milk & Metabolic Bone Disease

While human milk provides unmatched immunological and trophic benefits, unfortified mature human milk is nutritionally inadequate for preterm infants born at < 34 weeks gestation or < 1,500 grams.

Nutrient Deficits in Unfortified Human Milk

• Energy: Mature human milk provides ~20 kcal/oz (67 kcal/dL). At a standard full enteral volume of 150 mL/kg/day, unfortified milk delivers only 100 kcal/kg/day (falling short of the required 110–130 kcal/kg/day).
• Protein: Human milk contains ~0.9–1.2 g/dL of protein. At 150 mL/kg/day, this delivers only 1.5–1.8 g/kg/day of protein (less than half the required 3.5–4.5 g/kg/day), resulting in severe protein malnutrition, muscle wasting, and extrauterine growth restriction (EUGR).
• Calcium & Phosphorus: Human milk contains only ~25–30 mg/dL of calcium and ~15 mg/dL of phosphorus. At 150 mL/kg/day, this delivers ~38 mg/kg/day of Ca and ~22 mg/kg/day of P—vastly below third-trimester intrauterine accretion targets (150–220 mg/kg/day Ca and 75–140 mg/kg/day P).

Metabolic Bone Disease of Prematurity (MBDP / Osteopenia of Prematurity)

When preterm infants are fed unfortified human milk or inadequate mineral supplements, mineral depletion triggers a pathological homeostatic cascade:

+----------------------------------------------------------------------------------------------------+
|                           METABOLIC BONE DISEASE PATHOPHYSIOLOGY                                   |
|                                                                                                    |
|   Inadequate Enteral Ca & P Intake   -->   Severe Hypophosphatemia (Serum P < 4.5 mg/dL)            |
|   Hypocalcemia Triggers PTH Surge    -->   Secondary Hyperparathyroidism                            |
|   PTH Activates Osteoclasts          -->   Massive Skeletal Resorption & Bone Demineralization      |
|   Osteoblast Overactivity            -->   ELEVATED ALKALINE PHOSPHATASE (>800–1000 IU/L)           |
|   Clinical Consequences              -->   Pathological Fractures, Craniotabes, Rachitic Rosary,    |
|                                            Thoracic Instability & Prolonged Ventilator Dependence   |
+----------------------------------------------------------------------------------------------------+

Biochemical Screening & Diagnosis of MBDP

• Serum Alkaline Phosphatase (ALP): Routine screening starts at 4 to 6 weeks of life in VLBW infants. An ALP > 800 to 1,000 IU/L indicates active, severe osteoclast/osteoblast bone turnover and impending rickets.
• Serum Phosphorus: Serum phosphorus < 4.5 to 5.0 mg/dL (in the presence of normal renal function) is a sensitive early marker of phosphate depletion.
• Serum Calcium: Often remains deceptively normal or slightly low due to compensatory parathyroid hormone (PTH)-mediated calcium mobilization from skeletal bone stores.
• Radiological Findings: Demineralization, cortical thinning, cupping and fraying of the metaphyses (rachitic changes), and spontaneous rib fractures.

3. Human Milk Fortifiers (HMF): Types, Initiation & Caloric Targets

To overcome the nutritional deficits of unfortified milk, multi-nutrient Human Milk Fortifiers (HMF) are added directly to expressed maternal milk or donor human milk.

Classifications of Human Milk Fortifiers

1. Powdered Bovine-Based Fortifiers:
   • Concentrated packets added to human milk to increase caloric density, protein, calcium, phosphorus, electrolytes, trace minerals, and vitamins.
   • Clinical Consideration: Non-sterile powder; must be prepared under strict aseptic technique to prevent bacterial contamination (Cronobacter sakazakii).
2. Liquid Bovine-Based Fortifiers (Acidified vs. Non-Acidified):
   • Commercially sterile concentrated liquids.
   • Acidified Liquids: Extended shelf life, but lower pH may decrease protein solubility and cause metabolic acidosis or feeding intolerance in vulnerable preterms.
   • Non-Acidified Liquids: Neutral pH, highly soluble, optimal tolerance.
3. 100% Donor Human Milk-Derived Fortifier (Prolacta):
   • Concentrated pasteurized donor human milk paste added to maternal or donor milk to achieve an exclusive human milk diet (EHMD).
   • Clinical Benefit: Randomized trials demonstrate that an exclusive human milk diet eliminates bovine protein exposure, resulting in a statistically significant reduction in NEC, surgical NEC, late-onset sepsis, and mortality in extremely low birth weight infants (<1,000g).

Fortification Protocols & Caloric Densities

• Initiation Criteria: Initiate multi-nutrient fortification when enteral feeding volumes reach 100 to 120 mL/kg/day in infants born at < 34 weeks gestation or with a birth weight < 1,500 to 1,800 grams.
• Caloric Progression:
  • Standard baseline human milk = 20 kcal/oz (0.67 kcal/mL).
  • Initial fortification target = 22 kcal/oz (0.74 kcal/mL) for 24 to 48 hours to assess gastrointestinal tolerance.
  • Maintenance fortification target = 24 kcal/oz (0.81 kcal/mL), which satisfies full protein, calcium, and phosphorus goals at 150 mL/kg/day.
  • Concentrated fortification = 26 to 30 kcal/oz indicated for fluid-restricted infants with Bronchopulmonary Dysplasia (BPD), Congestive Heart Failure, or severe post-NEC malabsorption.

4. Comprehensive Formula Classification & Clinical Decision Matrix

When human milk is unavailable or contraindicated, specialized commercial infant formulas are selected based on gestational age, birth weight, metabolic capabilities, and underlying gastrointestinal pathology.

Clinical Matrix of Specialized Infant Formulas

5. Maternal Nutritional Needs During Lactation

The blueprint lists Maternal nutritional needs under Nutrition and Feeding, because the nurse counselling a mother expressing milk for a special care infant is counselling two patients.

Practical priority: the single strongest predictors of maintained supply for a mother separated from her infant are frequency of expression (8 or more times in 24 hours, including at least once overnight) and early initiation, not diet composition. Address the pumping schedule first, then nutrition.