4. Discussion
weight gain, sepsis, NEC
SEPSIS, PATHOGENESIS
Our study indicates that feeding hindmilk to very preterm infants with growth faltering may result in larger weight gain and higher weight and head circumference Z-scores after four weeks. Concentrations of fat and energy were significantly higher in hindmilk and were associated with improved weight and head size growth. Feeding hindmilk resulted in higher plasma EFAs, LA, and ALA. There was no difference in milk fatty acids distribution between hindmilk and composite milk. Although the pathogenesis of suboptimal extrauterine growth is multifactorial, variations in energy intakes could explain approximately 45% of the growth deficits in preterm infants [Fractionating breastmilk in our study resulted in approximately 1.4- and 1.16-fold increases in fat and energy of hindmilk content, respectively, compared with composite milk. This is in line with previous studies on the hindmilk of mothers of preterm infants [Our finding of increased weight gain is consistent with that in a previous study that used similar pre- and post-study design [It is worth mentioning that the effect of hindmilk in our study was temporary. The discharge weight z-score returned to values that were presented at the time of hindmilk introduction. The transitional period between 33–34 weeks corrected gestational age, which matches the endpoints in our study, and hospital discharge is complex in extremely preterm infants on respiratory support. Healthcare providers typically try weaning infants off nasogastric tubes and non-invasive respiratory support during this period. In addition, the type of fortification and other nutritional support are usually modified to facilitate hospital discharge. Some infants in our cohort required PN after the study endpoints due to morbidities including late-onset sepsis, NEC, and the need for surgical ligation to close the patent ductus arteriosus. Furthermore, most of the preterm infants in our cohort were transferred to level II NICUs before discharge. Unfortunately, we were not able to track nutritional intakes after the transfer. Using a mathematical approach, a 1.3 g fat/dL difference between analyzed composite milk and hindmilk results in an actual nutritional difference of 1.07 g of fat (83% of milk volume in 100 mL of fortified HM) and 9.6 Kcal/dL, after considering the fortification with liquid HMF and assuming relatively equal fluid intakes between pre- and post-hindmilk. Because the fat absorption in preterm infants is significantly lower than the fat absorption rate used to define metabolizable energy of the Atwater factor (70–80% in preterm infants versus 96% in adults) [Hindmilk is an attractive source of non-protein energy for improving growth in preterm infants because of its high energy density, lower osmolality compared with other fortification strategies, and its role in providing higher concentrations of soluble vitamins [Studies of optimal nutrition in preterm infants have primarily focused on the need for adequate protein intake to improve linear growth [There was a significant improvement in head circumference Z-score three and four weeks after feeding hindmilk. Previous studies on hindmilk did not reveal a significant change in head growth after hindmilk; however, these studies monitored head circumference for shorter durations [Plasma LA and ALA in our study increased by 1.1 and 1.3-fold, respectively, with no change in plasma ARA and DHA. LA and ALA are precursors for 