Composition of breast milk from mothers of premature and full-term infants and its influence in Z-Scores for infant physical growth

Background Breast milk contains various crucial nutrients and biologically active substances and is ideal for newborns. This study aimed to analyze the composition of breast milk from mothers of premature and full-term infants and its influences on the growth of infants. Methods Infant-mother dyads examined at our Hospital (March 2016 to May 2017) were included. Milk was collected at 0-1 month, 2-3 months, and 5-6 months and analyzed using a MIRIS human milk analyzer. Z-scores of weight-for-length (WLZ), weight-for-age (WAZ), and length-for-age (LAZ) were calculated. Results This study included full-term (>37 weeks of gestation, n=177) and premature (<37 weeks, n=94) infant-mother dyads. The premature infants showed higher Delta WAZ, Delta LAZ, and Delta WLZ from infancy to toddlerhood for the physical growth speed, compared with term infants (P<0.001). All proteins and true protein components of breast milk decreased with infants' age (P<0.001). For premature and full-term infants, differences in Delta WAZ and Delta LAZ from birth to infancy and the difference in Delta LAZ, WAZ, and LAZ in toddlerhood were positively associated with non-protein nitrogen (NPN) (all P<0.05), while the Z-score differences in Delta WLZ from birth to infancy were negatively associated with NPN (all P<0.05). For premature babies, from birth to infancy stage, Delta WAZ was positively correlated with NPN and carbohydrates while negatively correlated with dry matter (all P<0.05), and Delta LAZ correlated with NPN (beta=0.428, P=0.005). Conclusion Breastfeeding helped premature infants compensatory growth when compared to term infants. Whileduring early infancy stage Delta WLZ gain was negatively associated with increased amounts of NPN in breast milk. This might mean although NPN increase the Z-scores of weight-for-age and length-for-age, with no rise in adipose tissue mass.