The content of macronutrients in milk from mothers of very preterm infants is highly variable.

INTRODUCTION: The objective of this study was to determine the content of macronutrients in human milk (HM) from mothers who gave birth very prematurely, and to investigate possible associations between macronutrients and certain maternal and infant characteristics.

MATERIAL AND METHODS: Mothers of very preterm infants with a gestational age (GA) below 32 weeks expressed milk for analysis two weeks after birth, every second week until discharge, at term, at two, and at four months of corrected age. The milk was analyzed using mid-infrared transmission spectroscopy.

RESULTS: A total of 214 mothers delivered 736 HM samples for analysis. Two weeks after birth, protein content varied from 1.06 to 2.96 with a mean of 1.76 g/100 ml HM, and the mean protein content decreased significantly until eight weeks after birth (p < 0.04). Previous breastfeeding experience was associated with a lower protein content (p = 0.04) two weeks after birth. HM from mothers of extremely preterm infants (GA < 28 weeks) had a higher fat and energy content two weeks after birth than infants with a GA of 28-32 weeks (p = 0.001).

CONCLUSION: Protein content in human milk varies considerably between mothers, and decreases within weeks after very preterm birth. Previous breastfeeding experience and low GA were associated with a lower protein and a higher fat and energy content in HM, respectively. Inter-individual differences in human milk content possibly influences nutrition and this raises the question of the need for an individualized approach when fortifying human milk for preterm infants.

FUNDING: This study was funded by the Clinical Institute at the University of Southern Denmark and The Dagmar Marshall Foundation.

TRIAL REGISTRATION: Approved by the Danish National Committee on Biomedical Research Ethics (J.no. VF20030208).