Growth and Nutrition in the NICU

NICU Nutrition: More Than Just Feeds

If you work in the NICU long enough, you start to realize something important. Nutrition is not just supportive care. It is treatment.

For premature infants, nutrition is one of the most powerful therapies we provide. These babies are born during a time when the placenta would normally deliver large amounts of protein, calories, calcium, and phosphorus. When birth interrupts that process, the NICU team has to recreate those conditions as best as possible outside the womb.

That means every nutrition decision matters. Total fluids, calorie density, protein intake, fortification, and laboratory monitoring all work together to support growth. The goal is not simply to help babies gain weight. The goal is to support brain development, bone mineralization, and long term health.

And that is why NICU nutrition is far more complex than simply increasing feeds.

The challenge of growing outside the womb

During the third trimester, a fetus grows rapidly. Most of the body’s mineral stores and a large portion of brain growth occur during this period.

When a baby is born prematurely, that growth still needs to happen. It just happens in an incubator instead of in the uterus.

Because of this, premature infants have significantly higher nutritional needs than term babies. Many require approximately 110 to 130 kcal/kg/day to support growth. Protein intake is also critical because it supports lean body mass and brain development.

But there is a challenge. These babies often cannot tolerate large feeding volumes early in life. Many also have medical conditions that limit how much fluid they can safely receive.

That means the NICU team must constantly balance two things. How much fluid can safely be given, and how much nutrition the baby needs to grow.

Why fortification is so important

Human milk is the preferred feeding source for premature infants. It provides immune protection, supports gut development, and reduces the risk of necrotizing enterocolitis.

But human milk alone usually does not meet the nutritional needs of very premature infants.

This is where human milk fortifier comes in. Fortification increases calories, protein, calcium, and phosphorus so that premature infants can receive the nutrients they need for growth and bone development.

Fortification often begins when enteral feeds reach around 80 mL per kilogram per day. Many infants will then progress to 24 kcal feeds as feeding volumes increase.

A common misconception among newer nurses is that 24 kcal feeds are considered high calorie feeds.

In reality, 24 kcal per ounce is often the baseline for many NICU babies.

Many infants require even higher calorie concentrations such as 27 to 30 kcal per ounce. This is especially common in babies with bronchopulmonary dysplasia, congenital heart disease, or fluid restrictions. These babies need more calories but cannot tolerate larger fluid volumes, so increasing calorie density becomes essential.

Growth is the real outcome we are watching

While nutrition orders and feeding volumes are important, the real question is simple.

Is the baby growing?

NICU growth targets are designed to approximate the rate of growth that would normally occur during the third trimester.

Typical expectations include:

·Weight gain of about 15 to 20 g/kg/day in very premature infants

·Length increases of about 1 centimeter per week

·Head circumference growth of about 0.5 to 1 centimeter per week

It is important to remember that weight alone does not tell the whole story. Length and head circumference provide valuable information about overall growth and brain development.

Growth is usually tracked using specialized growth charts. Many NICUs use the Fenton growth chart for premature infants and transition to WHO growth charts as babies approach term age.

What matters most is not a single measurement but the trend over time.

When growth does not go as expected

When babies are not growing as expected, the nutrition plan often needs adjustment.

Poor growth may occur for several reasons. The baby may not be receiving enough calories or protein. Fluid restrictions may limit feeding volumes. Medical conditions such as infection, lung disease, or congenital heart disease can also increase metabolic demand.

Sometimes the baby is technically receiving enough calories on paper but still not growing well. In these situations, the team may increase calorie density or adjust fortification.

This is where the expertise of the NICU dietitian becomes incredibly valuable.

The role of the NICU dietitian

NICU dietitians are essential members of the care team.

They evaluate growth trends, calculate calorie and protein requirements, and recommend adjustments to feeding plans. They also monitor micronutrients and help guide supplementation with vitamins and minerals.

Dietitians often work closely with neonatologists, nurse practitioners, nurses, and pharmacists to ensure nutrition plans support optimal growth.

Many NICUs also hold regular nutrition rounds where growth data, laboratory values, and feeding tolerance are reviewed together.

Why laboratory monitoring matters

Laboratory monitoring plays an important role in evaluating nutrition.

Certain labs help identify whether babies are receiving adequate nutrients. For example, blood urea nitrogen can reflect protein intake. Electrolytes provide insight into fluid and metabolic balance.

Bone health is another critical area to monitor. Premature infants are at risk for metabolic bone disease because they miss much of the calcium and phosphorus transfer that occurs during the third trimester.

Elevated alkaline phosphatase levels and low phosphorus levels can signal impaired bone mineralization. Early detection allows the team to adjust nutrition and supplementation before fractures or other complications occur.

The big picture

NICU nutrition is complex because it sits at the intersection of physiology, growth, and disease.

Every day the care team balances fluids, calories, feeding tolerance, laboratory data, and growth trends. Each decision is made with the same goal in mind.

Helping babies grow safely.

For NICU nurses, understanding the reasoning behind nutrition decisions makes it easier to recognize when something is not right. Whether it is slow growth, feeding intolerance, or concerning lab values, these observations help guide the next step in care.