Science You Can Use: Do preemies need formula for adequate growth?

Did you notice this headline last month?  “Tiniest babies may need formula along with breast milk.”

That article was prompted by a new study on very low birth weight (VLBW) infants which concluded that while these infants can grow appropriately on fortified human milk:

VLBW infants fed >75% human milk are at greater risk of poor growth than those fed less human milk. This risk may be highest in those fed predominantly donor human milk.

I had heard that babies grew more slowly on donor milk than on formula, but I also know that formula puts preterm babies at higher risk for serious complications like necrotizing enterocolitis (NEC) and late onset sepsis.  And I’m a little puzzled by how we know what “normal,” healthy growth is for a tiny preemie, when until recently babies born this small just didn’t survive.  Obviously, this study raised a lot of questions.

So I was thrilled when Dr. Kathie Marinelli agreed to help sort this out.  Dr. Marinelli is a neonatologist at Connecticut Children’s Medical Center, and Associate Professor of Pediatrics at the University of Connecticut School of Medicine.  She’s also the Chair-Elect of the United States Breastfeeding Committee, on the board of the Academy of Breastfeeding Medicine, and Connecticut Chapter Breastfeeding Coordinator for the American Academy of Pediatrics.

Here are the questions I posed to her:

Since until recently VLBW babies generally didn’t survive, how is “normal” growth for these babies understood?  Is it based on the in utero growth rate?  For healthy term babies, the breastfed baby’s growth would be considered the norm.  Is that true for VLBW babies?

VLBW babies (those less than 1500 gms or 3 lbs 5 oz) have been surviving now for about 20 years, but certainly they have much better survival with less morbidity now than they did then due to improvements in many aspects of care, most notably both respiratory support for immature lungs and nutritional support.  The nutritional support includes improvements in intravenous nutrition, both the formulation of that nutrition and the fact that we start it within hours of birth, including protein, carbohydrate, fats, minerals and vitamins just like the placenta has been doing all along, instead of waiting several days only giving sugar like we used to do.  But maybe even more importantly we feed these babies using their GI tracts starting on the first or second day of life, when we used to not feed them sometimes enterally (via the GI tract) for weeks!

And we have learned through a tremendous amount of research that human milk—mother’s own milk (MOM) and donor human milk (DHM) are by far the best forms of nutrition for these babies (as they are for all babies).  No one really knows what “normal” growth is for premature babies.  It is not “normal” to be born early, and with either IV nutrition or enteral nutrition, we seldom do as well as the placenta does in growing these babies.  For many years we have assumed that “normal” growth for the premature baby is the growth they would have had if they had remained inside mom because that seems to make sense.  But we don’t really know.  We do know that human milk does not have the same amount of protein or calcium and phosphorus in it that the placenta delivers to the fetus.  So for the tiniest of babies who can’t just increase their intake to take more volume, if they receive only human milk, they do not grow.  That is why the milk is as we say “fortified”.  This means we add a pre-made mixture of protein, some fat, minerals for bone growth, and vitamins.  Premature formula is made with these things in it as well because term baby formula does not support the growth of these tiny babies either.  So that is important to know—no matter what they are fed, it needs extra protein, minerals and some calories as well.  So to the question as you asked it—we don’t know for sure what normal growth for these babies should be.  We make the assumption it should be like they were still in mom, but we have no proof for that at all!

If formula use is associated with faster growth, but also associated with higher risk of NEC, sepsis, and other problems, how do you balance these risks?

Formula use is associated with faster growth because the babies always get exactly the same amount of protein, calories and minerals, which are purposely higher in preterm formula, and we know how much because it is made, and the amounts are measured and put on the label.  But remember, we don’t for sure know that faster growth is better.  Look at term babies.  Formula fed babies grow faster—and now we are dealing with an obesity epidemic.

Now with premature babies, we do worry that if they don’t grow, especially their heads, which is a proxy for the growth of their brains, they may not develop normally.  So we walk a fine line between enough growth with them, and the complications that are increased when they do not receive human milk.  The research is very clear that premature babies who receive human milk (MOM or DHM or both) have significantly less incidence of necrotizing enterocolitis (devastating disease of the GI tract causing serious morbidity and even death); serious infections like sepsis and meningitis; both incidence and severity of retinopathy of prematurity (eye disease that causes blindness); as well as a number of other things like decreased incidence of readmission to the hospital for respiratory diseases in the first year of life.  There is also significant data that human milk fed premature babies have better neurodevelopmental outcomes (both mental and motor), which considering that by being born prematurely they are at risk for neurodevelopmental delays, is extremely important.  And all these results are dose dependent—meaning the more human milk they receive, the better protected or better their outcomes are.  So as the American Academy of Pediatrics states in its most recent statement on Breastfeeding and the Use of Human Milk, all babies, including premature and sick babies, should be fed human milk!  There is no question of balancing risks—the balance is totally in favor of human milk.  The caveat is that the tiniest babies need fortifier to help them grow.

What do you think the implications of this study are for the feeding of VLBW babies, and in particular for the use of donor milk?  Is the take away message:  formula is necessary for the growth of VLBW infants?

There is definitely no take away message that formula is necessary for the growth of VLBW infants.  And even the authors do not state that.  If you look carefully at the data, all groups of babies, regardless of how much human milk they received, had a decrease in their “z-score” from birth to discharge (a statistical way of looking at weight standardized for gestational age).  The only significant difference in growth was between babies receiving >75% of their feeds as human milk compared with all those babies grouped together receiving less than 75%.  It “trends” toward less growth in those babies fed predominantly donor milk, but was not significantly different.

As the authors point out, these results are likely because human milk is lower in protein (and minerals) than the artificially made formula, and donor milk comes from mostly moms who have had full-term babies within a year of delivery, which is even lower in protein.  The nutritional components of human milk (MOM or DHM) are not routinely measured, so when we add fortifier, we are “guessing” at what “average” human milk has in it, and then adding a standard formulation.

As we have been discussing at Connecticut Children’s Medical Center, work needs to be done on analyzing what exactly is in an individual mother’s milk, or donor milk batches, and then the possibility of fortifying individually to that particular baby becomes a possibility, which may lead to better growth.  This is all in the realm of active research right now, and if this practice is initiated sometime in the future, long-term outcome studies of growth and neurodevelopment will need to occur to make sure we are doing the best we can by these tiny babies.

One thought on “Science You Can Use: Do preemies need formula for adequate growth?

  1. I agree that MOM needs to be tested sooner as a mom of a Tetrology of fallot 27w 590g. My milk wasn’t tested till right before we went home. They had been giving him 3 packets of fortifier and discovered I made 31.5cal/oz. They imedeately dropped all fortifier and quit talking about feeding tubes. He was nursing like a champ but couldn’t take bottles. Over 2 years later, I still worry about all that unnecessary fortifier.


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