Mother’s own milk: A moving target | LATCH

Author: Amy Mailand Paradis ,NNP

Mother’s own milk (MOM) is the gold standard nutrition for all infants, but especially in the very-low-birth-weight (VLBW) infant in the neonatal intensive care unit (NICU). One of the challenges clinicians face is supporting adequate growth for VLBWs. Several studies have shown that MOM is highly variable in macronutrient content (carbohydrates, fats, and protein) and that human milk composition is dynamic. Standard fortification strategies assume that breastmilk is 20 kcal/oz, but two recent studies examine how the high variability in MOM may contribute to inconsistent growth. One study tracked the macronutrient variability in maternal milk over the course of 6 weeks.1

Researchers at University of Louisville analyzed 87 samples of milk collected from 20 mothers between 8 days and 6 weeks postpartum. All mothers had given birth to preterm babies weighing less than 1500 grams. The data showed that macronutrients varied widely from mother to mother and changed over the course of lactation. Surprisingly, the energy content ranged significantly from 9.5 to 30.4 kcal/oz across the study samples. The most interesting finding was that over two-thirds of the samples were less than 20 kcal/oz, of which 25% had less than 17 kcal/oz. Protein, an essential component of preterm nutrition, was also lower than expected (less than 1.5 g/dL) and it continued to decline over the study period. Fat content varied as well, but lactose remained fairly constant. Another similar study supported these findings: Dr. Charles Sauer and colleagues at the University of California San Diego studied 64 samples from 24 mothers of babies in the NICU over a course of 3 weeks.2

Maternal population mean age was 32 years, mean birthweight was 1767 grams, and age of gestation was 31 weeks. Inter-mother and intra-mother comparisons of macronutrients were conducted on frozen-then-thawed maternal milk. Again, the calorie content was lower on average (17.9 kcal/oz) than the assumed baseline of 20 kcal/oz for MOM. Only 34% of the samples were in the expected range of 18-22 kcal/oz. Less than half of the preterm milk samples were in the desirable range, whereas 38% of the samples were lower than anticipated. Protein decreased considerably over the study period, and fat content varied most widely. Postnatal growth failure has been linked to long-term neuro-developmental delay. These studies highlight the importance of fortification and the challenges clinicians face in meeting the macronutrient goals of preterm nutrition. Understanding the variation of maternal milk may help clinicians understand why postnatal growth failure continues to be a concern in the VLBW population as well as why increasing fortification early and up to higher content with human milk products is necessary to achieve acceptable growth patterns.

References

1. Arnold M, Adamkin D, Radmacher, P. Improving fortification with weekly analysis of human milk for VLBW infants. J Perinatol. 2017;37:194-196.
2. Sauer C, Boutin M, Kim J. Wide variability in caloric density of expressed human milk can lead to major underestimation or overestimation of nutrient content [published online December 1, 2016]. J Hum Lact. doi:10.1177/0890334416672200