Reasons Why Preterm Infants May Not Gain Weight and How to Address Them

Weight gain in preterm infants is a major concern for parents and caregivers. When a premature baby isn't gaining weight as expected, it's essential to investigate potential underlying causes. Healthy growth is crucial during the early weeks and months after birth, especially for babies born before 37 weeks of gestation. Several factors can contribute to poor weight gain, ranging from feeding issues to medical conditions. Understanding these factors can help parents and healthcare providers take timely action to support the infant's development.

Inadequate Milk Intake

One of the most common reasons for insufficient weight gain in preterm infants is inadequate milk intake. After discharge from the hospital, many parents choose direct breastfeeding, which makes it difficult to measure exactly how much milk the baby consumes. To monitor feeding more accurately, experts recommend expressing breast milk into a bottle during the first week at home. This allows caregivers to track the exact volume consumed per feeding and adjust as needed.

If measuring milk intake directly isn't possible, monitoring urine output is a reliable alternative. A well-fed preterm infant should have at least 8 to 10 wet diapers per day. Consistently low urine output may indicate that the baby isn't getting enough nutrition and requires closer evaluation by a pediatrician.

Type of Nutrition: Choosing the Right Feeding Strategy

Breast milk remains the gold standard for feeding preterm infants due to its optimal balance of nutrients and immune-boosting properties. However, standard breast milk contains about 67 kcal per 100 ml, which may not be sufficient for some underweight or slow-growing preemies.

Enhancing Breast Milk with Fortifiers

To increase caloric density, doctors often recommend adding a human milk fortifier (HMF) to expressed breast milk. This supplement boosts the energy content to approximately 81 kcal per 100 ml, supporting better weight gain without compromising the benefits of breastfeeding.

Alternative: Specialized Preterm Formulas

When breastfeeding isn't an option, specialized post-discharge formulas designed for premature infants are available. These formulas typically provide around 73 kcal per 100 ml and are enriched with essential proteins, vitamins, and minerals tailored to the needs of growing preemies. Transitioning to such formulas can significantly improve growth outcomes.

Underlying Infections

Preterm babies have immature immune systems, making them more vulnerable to infections—both bacterial and viral. Poor weight gain can often be one of the earliest signs of an underlying infection, even before fever or other obvious symptoms appear.

Common sources of infection include respiratory illnesses, urinary tract infections, and gastrointestinal bugs. If a baby shows signs of lethargy, poor feeding, temperature instability, or irritability alongside stalled weight gain, prompt medical assessment is critical. Early diagnosis and treatment can prevent complications and restore normal growth patterns.

Anemia and Its Impact on Growth

Anemia is highly prevalent among preterm infants due to several factors: shorter red blood cell lifespan, limited iron stores transferred from the mother, and rapid growth demands. Severe anemia can lead to fatigue, reduced feeding efficiency, and decreased oxygen delivery to tissues—all of which hinder proper weight gain.

Routine screening for anemia is recommended in preemies, and interventions may include iron supplementation, erythropoietin therapy, or, in severe cases, blood transfusions. Addressing anemia effectively not only improves energy levels but also supports steady weight progression over time.

In conclusion, while slow weight gain in preterm infants can be concerning, identifying and managing the root cause—whether nutritional, infectious, or hematological—can make a significant difference. Close collaboration with neonatal care teams, regular follow-ups, and attentive home monitoring empower parents to give their premature babies the best chance for healthy growth and long-term development.