Changes in preterm breast milk nutrient content in the first month

The primary aim of the study was to investigate the changes in composition of breast milk from mothers with preterm infants (gestation age < 35 weeks) during the first 4-6 weeks of lactation.

Breast milk from 17 mothers who had delivered preterm infants was collected longitudinally for 4-6 weeks. Breast milk from 15 mothers of full-term infants was also collected at the 1(st) week and 4(th) week. Fat, protein, lactose, energy, minerals (calcium and phosphate), and immune components [secretory immunoglobulin A (IgA), leptin, lysozyme, and lactoferrin] content were measured weekly in each participant. A mid-infrared human milk analyzer was used to measure the protein, fat, and lactose contents. Calcium and phosphate components were checked via spectrophotometry. The concentrations of major immune components (secretory IgA, lactoferrin, lysozyme, and leptin) were quantified using enzyme-linked immunosorbent assay kits.

Eighty samples from 17 preterm mothers were collected. The mean gestational age was 29.88 ± 2.39 weeks. There were significant changes in nutrient components during these periods, with increases in lactose (p < 0.001), lipid (p = 0.001), calorie (p = 0.012), and phosphate (p = 0.022) concentration and decreases in protein (p < 0.001) and secretory IgA (p < 0.001) concentration. There were no differences in calcium (p = 0.919), lactoferrin (p = 0.841), leptin (p = 0.092), and lysozyme (p = 0.561) levels. Furthermore, there were no significant differences in most components of breast milk between full-term and preterm mothers.

The longitudinal study revealed significant changes in macronutrient contents and secretory IgA concentration in preterm milk over the 4-6 week period, which is compatible with the results of previous studies. The quantification of phosphate in preterm breast milk was lower than the normal range, suggesting that close monitoring of body bone mass may be indicated. More studies are warranted to evaluate the clinical significance of alterations of major milk components during the postnatal stage.