Duration of Breast Milk Fortifier for Low Birth Weight Infants
Breast milk fortifier should be continued until hospital discharge or 40 weeks postmenstrual age (whichever comes first) for very low birth weight infants, with some evidence supporting continuation until 52 weeks postmenstrual age for optimal catch-up growth.
Primary Recommendations by Birth Weight Category
Very Low Birth Weight (<1500g) and Preterm (<32 weeks)
Fortification should continue until at least 40 weeks postmenstrual age or hospital discharge, as this represents the standard endpoint used in clinical trials demonstrating improved growth outcomes 1, 2.
Research demonstrates that fortification periods of 3-4 weeks minimum are necessary to achieve adequate weight gain (15-25 g/kg/day) in VLBW infants 3, 1, 2.
After hospital discharge, transition to preterm follow-up formulas (24-30 kcal/oz) is recommended to continue meeting the higher nutrient requirements as infants approach 1 year of age 4.
Low Birth Weight (1500-2000g)
Iron supplementation (2-3 mg/kg/day) should continue for at least 6 months starting between 2-6 weeks of age, as these infants have lower iron endowment at birth 4.
For breast-fed preterm or low birth weight infants, the CDC recommends 2-4 mg/kg/day of iron drops (maximum 15 mg/day) starting at 1 month after birth until 12 months 5.
Marginally Low Birth Weight (2000-2500g)
- Iron supplementation at 1-2 mg/kg/day should continue for at least 6 months to prevent iron deficiency anemia 4.
Rationale for Extended Fortification
The extended duration is necessary because:
VLBW infants require 120-150 kcal/kg/day or more to achieve catch-up growth, which cannot be met by breast milk alone (0.62 kcal/g) 4.
Breast milk composition is highly variable, with all 650 pooled samples in one study requiring at least one macronutrient adjustment to meet target levels 3.
Standard fortification alone often results in extrauterine growth restriction, with 73-81% of infants falling below the 10th percentile on growth charts despite fortification 1.
Monitoring and Adjustment
Assess growth velocity weekly: Target weight gain should be 15-25 g/kg/day for VLBW infants 3, 1, 2.
Monitor for feed intolerance: Fortification may need temporary interruption if significant intolerance develops, though preterm formula powder fortification shows lower intolerance rates (1.4 vs 6.8 per 1000 patient-days) compared to commercial fortifiers 1.
Transition timing: When exclusive breastfeeding stops or at 6 months (whichever comes first), ensure continued iron supplementation of approximately 1 mg/kg/day, preferably from supplementary foods 5.
Common Pitfalls to Avoid
Do not discontinue fortification prematurely based solely on reaching full enteral feeds; continue until discharge or 40 weeks postmenstrual age 1, 2.
Do not assume breast milk alone is sufficient for LBW infants even after initial weight recovery, as they require enhanced nutrition for catch-up growth 4, 3.
Avoid exceeding recommended osmolality (target <450 mOsmol/kg) when fortifying, as this increases risk of feed intolerance 3.
Do not forget iron supplementation after fortification ends, as LBW infants remain at high risk for iron deficiency through at least 6-12 months of age 4, 5.