Metabolic abnormalities at birth include congenital hypothyroidism, galactosemia, congenital adrenal hyperplasia, hemoglobinopathies, phenylketonuria, hypoglycemia, and hypocalcemia.
Do You Understand Neonatal Metabolic Disorders? (Public Health Network)
Hypothermia
Abnormally low body temperature.A newborn's environmental temperature is influenced by relative humidity, airflow, proximity to cold surfaces (radiative heat loss), and ambient temperature. Infants are prone to hypothermia in cold environments, which can lead to hypoglycemia, metabolic acidosis, and death. Due to their high body surface area-to-weight ratio, radiative heat loss occurs rapidly, particularly affecting low birth weight infants.Evaporative heat loss (e.g., when newborns are soaked in amniotic fluid in delivery rooms), along with conductive and convective heat loss, can result in substantial heat loss and cause hypothermia even in relatively warm rooms.
Increased oxygen demand (metabolic rate) due to cold stress can also cause tissue hypoxia and neurological damage in newborns with respiratory insufficiency (e.g., preterm infants with respiratory distress syndrome). Prolonged, unrecognized cold exposure diverts calories toward thermogenesis, impairing growth.
The neonatal response to cold involves sympathetic release of norepinephrine acting on "brown fat."This specialized tissue in newborns is located in the posterior neck, between the shoulder blades, and around the kidneys and adrenal glands. It responds by releasing fatty acids through lipolysis, followed by oxidation or re-esterification. These reactions generate heat locally, and the rich blood supply to brown fat aids in transferring heat to other body regions. This response increases metabolic rate and oxygen consumption by 2 to 3 times the baseline.
Prevention and Treatment
Hypothermia prevention involves promptly drying the newborn in the delivery room (preventing evaporative heat loss) followed by wrapping the infant in a warm blanket (including the head). If exposure is necessary for resuscitation, close observation, or skin-to-skin contact with the mother, radiant heaters should be used.
For ill newborns, a neutral environmental temperature must be maintained—an environmental state and temperature that minimizes the newborn's metabolic rate while preserving normal core temperature (37°C). Incubator temperature can be adjusted according to Table 260-2 based on the infant's birth weight and postnatal age to approximate neutral environmental temperature.Servo-controlled incubators or radiant heaters may also be used to maintain the infant's skin temperature at 36.5°C.
Hypothermia treatment involves rewarming the infant using an incubator or radiant heater, while monitoring for hypoglycemia and apnea.If hypothermia is not caused by cold environmental temperatures but rather by pathological conditions such as sepsis or intracranial hemorrhage, specific treatment is required.
Hypoglycemia
Blood glucose levels <40 mg/dL (<2.2 mmol/L) in term infants and <30 mg/dL (<1.7 mmol/L) in preterm infants.
Etiology
Hypoglycemia commonly arises from insufficient glycogen reserves at birth or secondary to hyperinsulinemia. Extremely low birth weight preterm infants have inadequate glycogen stores and are prone to hypoglycemia unless receiving continuous exogenous glucose infusion.Newborns with intrauterine growth restriction (IUGR) due to placental insufficiency (manifesting as small for gestational age) also lack glycogen reserves. If perinatal asphyxia and hypoxia persist, their entire glycogen stores are rapidly depleted through anaerobic glycolysis. Infants with insufficient glycogen reserves may develop hypoglycemia at any time during the first few days of life, particularly when feeding intervals are prolonged or nutrient intake is inadequate.
Hyperinsulinemia occurs in newborns of diabetic mothers (in inverse proportion to diabetes control), those with severe nucleated erythrocytosis, or those with Beckwith-Wiedemann syndrome (characterized by macrosomia, umbilical hernia, and hypoglycemia).Elevated neonatal insulin levels characteristically cause a rapid decline in blood glucose within the first 1 to 2 hours after birth due to the abrupt cessation of continuous glucose supply from placental sources. Hypoglycemia may also occur in infants following sudden discontinuation of intravenous glucose infusion.>While many hypoglycemic newborns are asymptomatic, manifestations such as lethargy, poor feeding, hypotonia, irritability, apnea, tachypnea, or seizures may occur. These signs are nonspecific and can also be seen in infants with a history of asphyxia, sepsis, hypocalcemia, or withdrawal syndromes (e.g., anesthetic withdrawal).
The relationship between these signs, hypoglycemia, and subsequent neurological impairment remains unclear.
Prevention and Treatment
Given that neonatal hypoglycemia can cause neurological damage, prevention and prompt treatment are essential.
Infants born to mothers with insulin-dependent diabetes mellitus frequently develop hypoglycemia after birth, often accompanied by poor feeding. Therefore, immediate intravenous infusion of 10% glucose solution is indicated at birth, as is the case for infants with other diseases, extreme prematurity, or respiratory distress. For other infants at risk for hypoglycemia but without disease, early initiation of frequent formula feedings is recommended to provide carbohydrates and other nutrients.Additionally, all such newborns require regular blood glucose monitoring. Point-of-care testing can be performed using diagnostic glucose test strips (e.g., Chemstrip bG). However, capillary blood glucose measurements using glucose oxidase test strips are insufficiently accurate. Any newborn with blood glucose values at the lower limit or exhibiting symptoms suggestive of hypoglycemia should undergo laboratory testing to determine true blood glucose levels.
Newborns exhibiting hypoglycemia symptoms or those whose blood glucose cannot be rapidly elevated via enteral feeding should immediately receive intravenous infusion of 10% glucose solution at 5 ml/kg over 10 minutes or longer. Subsequently, glucose should be administered at a rate of 4–8 mg/(kg·min) [equivalent to 60–120 ml of 10% glucose solution/(kg·day)]. Adjust infusion rates based on glucose level monitoring.Once the newborn's condition improves, gradually replace intravenous fluids with enteral feeding while continuing blood glucose monitoring. Reduce intravenous glucose gradually, as abrupt discontinuation may cause hypoglycemia. If immediate intravenous glucose administration is difficult for hypoglycemic newborns, intramuscular injection of 100–300 μg/kg glucagon (maximum 1 mg) often rapidly elevates blood glucose levels;unless glycogen stores are depleted, with effects lasting 2–3 hours. For hypoglycemia unresponsive to rapid glucose infusion, administer hydrocortisone 5 mg/(kg·d) in two IM doses. Consider alternative causes (e.g., sepsis) and perform endocrine evaluations for refractory hypoglycemia.
Hyperglycemia
Neonatal blood glucose >120 mg/dL(6.7 mmol/L).
The incidence of hyperglycemia is lower than that of hypoglycemia. However, extremely low birth weight infants (<1.5 kg) may develop severe hyperglycemia within the first few days of life following rapid glucose infusion. Hyperglycemia may also occur in infants experiencing severe stress or sepsis, particularly those with fungal sepsis.
Transient neonatal diabetes is a rare, self-limiting hyperglycemia commonly seen in small-for-gestational-age infants. Hyperglycemia may cause glycosuria with osmotic diuresis and dehydration. Severe hyperglycemia with markedly elevated blood osmolarity can lead to neurological damage.
Treatment
For iatrogenic cases, management includes reducing the infusion rate of glucose solution (simultaneously lowering concentration from 10% to 5% or slowing intravenous flow) and correcting fluid and electrolyte losses from osmotic diuresis via intravenous replacement.Persistent hyperglycemia during low-rate glucose infusion (e.g., 4 mg/kg/min) suggests relative insulin deficiency or insulin resistance. Human insulin may be added to 10% glucose solution at a standard infusion rate of 0.01–0.1 U/kg/h until blood glucose normalizes. Insulin can be administered in a separate 10% glucose solution alongside the maintenance infusion to facilitate dose adjustment.(U/kg·h) until blood glucose levels normalize. Insulin may be added to a separate 10% glucose solution and administered alongside the maintenance infusion of 10% glucose, allowing adjustment of the infusion rate without altering the overall venous fluid delivery rate. The response to insulin therapy is unpredictable, making careful monitoring of blood glucose levels and precise insulin rate adjustment critical.
For neonatal transient diabetes, careful maintenance of glucose homeostasis and fluid balance is required until hyperglycemia resolves spontaneously, typically taking several weeks.
Hypocalcemia
Serum total calcium concentration: Term infants <8 mg/dL (<2 mmol/L), preterm infants <7 mg/dL(＜1.75 mmol/L); may also be determined by ionized calcium concentration based on the assay method (electrode type) used; Ca＜3.0–4.4 mg/dL (＜0.75–1.10 mmol/L).
Hypocalcemia is quite common among newborns in neonatal intensive care units. High-risk groups include preterm infants, small-for-gestational-age infants, newborns of diabetic mothers, and those with a history of perinatal asphyxia.
Etiology