An Update on Neonatal Hypoglycemia

Glucose is the predominant source of energy for the fetal and neonatal brain. During the process of adaptation from a continuous supply of glucose in-utero to an intermittent supply after birth, the neonate is prone to periods of low blood glucose. Transient mild decreases in blood glucose levels are a common feature of perinatal adaptation. This period is characterized by an up-regulation of hormonal and metabolic pathways of gluconeogenesis, hepatic glycogenolysis and ketogenesis. However, in some neonates, these may be delayed and hypoglycemia may get prolonged or severe. Persistent, recurrent or severe hypoglycemia may cause irreversible injury to the developing brain. Hence, the neonatologist needs to be proactive in suspecting, diagnosing and treating hypoglycemia in the newborn. The normal range of blood glucose is different for each newborn and depends upon birthweight, gestational age, body stores, feeding status, availability of energy sources as well as the presence or absence of disease. Population based meta-analyses have revealed that the blood glucose levels rise with increasing post natal age. Although, there are controversies surrounding the definition, a blood glucose <40 mg/dL is considered as the operational threshold to treat hypoglycemia in all neonates in first few days of life, irrespective of gestation. Hypoglycemia is the most common metabolic disorder in the neonatal intensive care unit. The reported incidence of hypoglycemia varies with the definition, population, glucose measurement technique and feeding schedule. Preterm infants and those with intrauterine growth retardation are at a high risk of developing hypoglycemia in the first week of life because of lack of sufficient glycogen and fat stores, which are normally accumulated in the third trimester. In some preterm infants, developmental delays in the postnatal up-regulation of enzymes of glucose homeostasis may persist even at the time of discharge from hospital. Large for gestational age infants and infants of diabetic mothers are the other important high risk groups because of relative hyperinsulinemia. A proportion of small for gestational age infants also have high insulin levels which contribute to hypoglycemia and can persist for few weeks to months. Recently, late preterm (340/7 to 366/7weeks) infants have been identified as another important group prone to hypoglycemia. In addition, any sick newborn warrants screening for low blood glucose. Term healthy infants without any risk factors need not be monitored routinely. All asymptomatic, at-risk neonates should be screened at two hours after birth and surveillance should be continued 4-6 hourly thereafter, until feedings are well established and glucose values have normalized; which may take 48-72 hours. Monitoring before 2 hours may be