Our smallest infants now deliver at birth weights well below 500g, which is just about the size of my adult hand.
Successfully surviving and growing a micro preemie is a modern day miracle. They start off being mostly water, with a mixture of soft tissue and bone, virtually no body fat, and limited muscle mass. This stage of life represents a significant nutritional emergency, and is an enormous hurdle in the first few months of life.
In relative terms, an adult would need to put on three pounds of weight gain daily to match the growth rate of a micro preemie. The growth of the micro preemie is the fastest at any point in its lifetime, including the rapid growth phase of adolescence. That is why even one day of inadequate intake is essentially starving our infants.
The immediate loss of weight represents both the loss of water and lean mass. This leads to a return to birth weight closer to 10-14 days, which is an automatic crossing of growth percentiles even before they can start to grow on their appropriate growth line. It is presently debatable whether the target for preterm infants is attaining their birth percentile or just continuing on this newly adjusted growth percentile line (I fall in the latter camp).
The importance of nutrition and brain development is clear. Poor growth is strongly associated with poor neurodevelopmental outcomes.1 If that is true, then why don’t we react to the malnutrition? First, I think we stop seeing it. For example, my home and office desks are always in a state of flux, going from clean to overtly messy. If my desk is messy for less than a week, the messiness will evoke a response in me to bring it back to a clean state. But if it is messy for more than a few weeks, it goes by unnoticed. In a similar way, I think far too many times we become desensitized and blind to the degree and amount of malnutrition we have in the NICU. On any given day I can walk through my own NICU and identify significant degrees of malnutrition in the unit.
The other reason may be that we think we are already doing our best, and so there is little room to do more. This is a fallacy for several reasons, but the biggest one to mention now is that we falsely assume that mother’s milk is textbook 20 kcal/oz and that content is according to textbook nutrition charts.2 How often are we wrong in attributing the calories and content of mother’s milk? Our nutrition strategy for fortification of mother’s milk might as well be random. If you examine random milk samples, more than half the time you are off base, sometimes overestimating and other times underestimating nutrient content. Mothers make samples that vary around twofold in energy content, and so half the time the overestimation is responsible for restriction of the nutrients these babies need.
Growth is compounding, and so if you are shy of the appropriate amount of nutrition and energy by 5% each day, you can quickly accumulate major deficits, even after a few weeks. This was nicely illustrated in the classic Embleton paper.3 We can take advantage of this when we are trying to catch up from recent poor growth by estimating in a daily compensation for the additional growth you desire. For a completely opposite reason, this is why if you consistently eat just a bit more than your body needs each day, the pounds will add up over time.
Growth charts are powerful tools that can assist our ability to optimally grow our babies. More than two decades ago, we used to plot infants on the IHDP growth charts in an effort to measure preterm infants against their previously grown peers. On these charts, the growth percentiles were so much better than if they were plotted on an in utero or birth weight-based growth chart.
We now know that we are only as good as our standard. Since the gold standard has remained the in utero growth rates, we have still more work to do. Electronic medical records can greatly improve our ability to view the growth trajectory of our infants, but most will plot on a weekly basis, which is far too long a stretch to react to poor growth in a preemie. I will typically respond to a three day growth pattern to minimize the growth, and this requires the readout of the daily weights to respond.
Given the large inaccuracies in our nutritional assumptions, it has always made sense to me to be more proactive in nutrition, especially with protein delivery. If you wait for an infant to grow poorly multiple times in early life, you accumulate deficits to recover from, and potentially may have limited the brain development at that stage in life. The use of our newer liquid human milk fortifiers that contain higher protein content, or higher caloric-dense donor milk-based human milk fortifiers are simple ways to build in such a preemptive response.
So there is never a bad time to take a good look around your unit and count the number of babies who are malnourished and who are failing to achieve their ideal growth rate. These represent the gap that you need to close more in the future. Only by paying attention and following the nutrient intake and growth data will we conquer being skinny in the NICU. Please keep the mantra going: Grow, baby grow!
1. Ehrenkranz RA, Dusick AM, Vohr BR, Wright LL, Wrage LA, Poole WK. Growth in the neonatal intensive care unit influences neurodevelopmental and growth outcomes of extremely low birth weight infants. Pediatrics. 2006 Apr;117(4):1253-61.
2. Sauer C, Boutin M, Kim JH. Wide Variability in Caloric Density of Expressed Human Milk Can Lead to Major Underestimation or Overestimation of Nutrient Content. J Hum Lact. 2016. In press.
3. Embleton NE, Pang N, Cooke RJ. Postnatal malnutrition and growth retardation: an inevitable consequence of current recommendations in preterm infants? Pediatrics. 2001 Feb;107(2):270-3.