Causes of Low Blood Sugar in Newborns: A Comprehensive Guide for Parents

Low blood sugar, or hypoglycemia, is a relatively common condition in newborn infants and can lead to serious health complications if not promptly addressed. Understanding the underlying causes is essential for early detection and effective management. While many babies experience mild and temporary drops in blood glucose shortly after birth, certain risk factors can increase the likelihood of more severe or prolonged hypoglycemia.

Common Medical Factors Behind Neonatal Hypoglycemia

Newborns are particularly vulnerable to fluctuations in blood glucose levels due to their developing metabolic systems. Several medical and physiological factors contribute to this vulnerability, especially in high-risk infants.

1. Premature Birth and Feeding Difficulties

Babies born prematurely often struggle with feeding because their sucking and swallowing reflexes may not be fully developed. This results in reduced milk intake during the first critical days of life, limiting glucose supply. Additionally, preterm infants have underdeveloped digestive systems, making it harder for them to absorb nutrients efficiently, further increasing the risk of low blood sugar.

2. Limited Glycogen Stores in Preterm Infants

Full-term babies typically build up glycogen reserves in the liver during the final weeks of pregnancy, which are then converted into glucose after birth to maintain energy levels. However, premature infants miss out on this crucial storage phase, leaving them with insufficient glycogen stores. As a result, they are unable to sustain normal blood glucose levels without frequent external feeding.

3. Birth Complications Such as Asphyxia or Infection

Infants who experience perinatal asphyxia (lack of oxygen around the time of birth) may suffer from impaired liver function, reducing their ability to produce and release glucose. Similarly, neonatal infections place significant stress on the body, increasing glucose consumption while simultaneously impairing production. Both scenarios can rapidly deplete available glucose, leading to clinically significant hypoglycemia.

4. Maternal Diabetes During Pregnancy

When a mother has gestational or pre-existing diabetes, her elevated blood glucose levels cross the placenta, prompting the fetal pancreas to produce excess insulin. After delivery, the baby is suddenly cut off from the high-glucose environment but continues to secrete high levels of insulin, causing a sharp drop in blood sugar. This condition, known as transient hyperinsulinism, is one of the most common causes of neonatal hypoglycemia.

5. Inherited Metabolic Disorders

Certain rare genetic conditions affect how a baby's body processes fats, proteins, or carbohydrates. Examples include fatty acid oxidation disorders and glycogen storage diseases. These metabolic abnormalities prevent the body from generating glucose effectively during fasting periods, making affected infants prone to recurrent episodes of hypoglycemia, even with regular feedings.

6. Hyperinsulinism Due to Pancreatic Abnormalities

Some newborns are born with congenital hyperinsulinism—a condition where the insulin-producing beta cells in the pancreas are overactive or abnormally increased in number. In more severe cases, pancreatic cell tumors (insulinomas) may be present. Both lead to excessive insulin secretion, driving glucose into cells and dangerously lowering blood sugar levels.

7. Endocrine and Hormonal Imbalances

Hypoglycemia can also stem from deficiencies in key hormones that regulate glucose metabolism. Conditions such as congenital hypothyroidism, adrenal insufficiency, or pituitary-hypothalamic dysfunction impair the body's ability to mobilize stored glucose. These endocrine disorders often require specialized diagnostic testing and long-term hormone replacement therapy.

Early recognition and intervention are vital in managing neonatal hypoglycemia. Symptoms like jitteriness, poor feeding, lethargy, or seizures should prompt immediate medical evaluation. Routine screening, especially in at-risk infants, combined with timely feeding support or intravenous glucose when necessary, can prevent neurological damage and ensure healthy development.