Blood sugar, or glucose, serves as the primary energy source for all bodily cells, especially the developing brain and organs of an infant. Maintaining a stable blood glucose level is important for healthy growth and development in newborns. While babies receive glucose through the placenta before birth, they rely on their own internal regulation and feeding after delivery. An infant’s metabolism is sensitive, making them susceptible to blood sugar fluctuations that can fall too low, a condition known as hypoglycemia.
Defining Hypoglycemia in Mature Infants
Hypoglycemia in a mature infant is defined by specific blood glucose thresholds. A plasma glucose level below 45 mg/dL (2.5 mmol/L) after the first 24 hours of life is considered hypoglycemia in asymptomatic term neonates. In the first 24 hours, a level below 30 mg/dL (1.65 mmol/L) is used. A “mature infant” refers to a full-term newborn, born between 37 and 41 weeks of gestation, who is of appropriate weight for their gestational age and whose tissues and organs are fully developed.
Maintaining stable blood sugar is important for an infant’s developing brain because glucose is its primary fuel. The brain of a newborn has higher glucose needs compared to adults due to rapid growth and metabolic demands. Prolonged or severe hypoglycemia can lead to serious consequences, including brain injury, seizures, and long-term neurodevelopmental problems such as intellectual disability, developmental delays, or learning difficulties.
Newborns are susceptible to blood sugar fluctuations during the transition from relying on the maternal glucose supply to managing their own glucose production and utilization. After birth, blood glucose levels reach their lowest point 1 to 2 hours after delivery before gradually rising as the baby’s body begins to use its own glucose and fat stores. An immature liver function can also contribute to these fluctuations, as the liver is responsible for producing glucose.
Signs and Causes of Low Blood Sugar
Recognizing signs of low blood sugar in an infant can be challenging, as symptoms are often subtle, non-specific, or absent. Parents should be aware of indicators such as jitteriness or shakiness, lethargy, poor feeding, and a weak or high-pitched cry.
More pronounced signs include pale or bluish-colored skin, sweating, low body temperature (hypothermia), and floppy muscles. In severe cases, infants might experience breathing problems such as pauses in breathing (apnea), rapid breathing, grunting sounds, or seizures. Because these symptoms can mimic other health conditions, it is important to seek medical attention for a proper diagnosis.
Several factors can contribute to hypoglycemia in a mature infant. Inadequate feeding is a common reason, as babies rely on milk (breast milk or formula) for their glucose supply after birth. Babies born to mothers with diabetes, particularly if the maternal diabetes was not well-controlled, may produce too much insulin, leading to low blood sugar after birth when the continuous glucose supply from the mother is removed.
Other causes include certain genetic conditions, infections (sepsis), or birth stress. Infants who are larger or smaller than expected for their gestational age, or those who experienced a lack of oxygen at birth (birth asphyxia), also face a higher risk. Sometimes, no clear cause is identified for transient low blood sugar in newborns.
Managing and Preventing Hypoglycemia
If low blood sugar is suspected or confirmed in an infant, immediate medical consultation is important. For infants who are able to feed, the first step involves offering breast milk or formula to increase blood glucose levels. Healthcare providers may also recommend giving an oral glucose gel rubbed inside the baby’s cheeks, an effective way to raise blood sugar.
If the infant is unable to eat by mouth, if feeding does not improve blood sugar, or if levels are very low, healthcare providers may administer intravenous (IV) glucose. This involves giving a sugar solution directly into a vein to quickly normalize glucose levels. Monitoring the baby’s blood glucose levels will continue until they can maintain stable levels on their own, which may take hours or even days.
Preventing hypoglycemia in healthy mature infants involves ensuring consistent and adequate feeding. Frequent feeding, whether breastfeeding or formula feeding, helps establish a steady supply of glucose and allows the baby to build up their own energy stores. Monitoring feeding patterns to ensure the baby is feeding effectively and taking in enough milk is beneficial. For at-risk infants, such as those born to mothers with diabetes, early and routine glucose checks are performed in the hospital. Discussing any risk factors with a pediatrician allows for proactive monitoring and intervention, ensuring the baby receives appropriate care to prevent or manage low blood sugar.