Pathophysiology
Clinical meaning
Neonatal hypoglycemia is defined as a blood glucose level below 2.6 mmol/L (47 mg/dL) in a newborn, though some guidelines use operational thresholds as low as 2.0 mmol/L for intervention in the first hours of life. Glucose is the primary energy substrate for the neonatal brain, and unlike adults, neonates have limited ability to produce alternative fuels (ketone bodies) during hypoglycemia. Prolonged or severe neonatal hypoglycemia can cause permanent neurological injury including seizures, cognitive impairment, and developmental delay. During fetal life, glucose is supplied continuously across the placenta via facilitated diffusion. The fetus maintains blood glucose levels approximately 60-70% of maternal levels. At birth, this continuous glucose supply is abruptly terminated when the umbilical cord is clamped. The neonate must rapidly transition from continuous placental glucose delivery to intermittent enteral feeding and endogenous glucose production. Normal metabolic transition involves several hormonal changes. Plasma glucagon rises within minutes of birth, while insulin levels fall. This hormonal shift activates hepatic glycogenolysis (breakdown of glycogen stores to release glucose) and gluconeogenesis (de novo glucose production from amino acids, lactate, and glycerol). Additionally, lipolysis...