(See also general discussion of hypocalcemia.)
Hypocalcemia is a total serum calcium concentration < 8 mg/dL (< 2 mmol/L) in term infants or < 7 mg/dL (< 1.75 mmol/L) in preterm infants. It is also defined as an ionized calcium level < 3.0 to 4.4 mg/dL (< 0.75 to 1.10 mmol/L), depending on the method (type of electrode) used. Signs are primarily neurologic and include hypotonia, apnea, and tetany. Treatment is IV or oral calcium supplementation.
Neonatal hypocalcemia occurs in 2 forms:
Some infants with congenital hypoparathyroidism (eg, caused by DiGeorge syndrome with agenesis or dysgenesis of the parathyroid glands) have both early and late (prolonged) hypocalcemia.
Risk factors for early-onset hypocalcemia include prematurity, being small for gestational age, maternal diabetes, and perinatal asphyxia. Mechanisms vary. Normally, parathyroid hormone helps maintain normal calcium levels when the constant infusion of ionized calcium across the placenta is interrupted at birth. A transient, relative hypoparathyroidism may cause hypocalcemia in preterm neonates and some small-for-gestational-age neonates, who have parathyroid glands that do not yet function adequately, and in infants of mothers with diabetes or hyperparathyroidism, because these women have higher-than-normal ionized calcium levels during pregnancy. Perinatal asphyxia may also increase serum calcitonin, which inhibits calcium release from bone and results in hypocalcemia. In other neonates, the normal phosphaturic renal response to parathyroid hormone is absent; the elevated phosphate level leads to hypocalcemia.
Symptoms and signs of neonatal hypocalcemia rarely occur unless total serum calcium is < 7 mg/dL (< 1.75 mmol/L) or the ionized calcium is < 3.0 mg/dL (< 0.75 mmol/L). Signs include hypotonia, tachycardia, tachypnea, apnea, poor feeding, jitteriness, tetany, and seizures. Similar symptoms may occur with hypoglycemia and opioid withdrawal.
Diagnosis of neonatal hypocalcemia is by measurement of total or ionized serum calcium; ionized calcium is the more physiologic measurement, because it does not require correction for protein concentration and pH. Prolongation of the corrected QT interval (QTc) on ECG also suggests hypocalcemia.
Early-onset hypocalcemia ordinarily resolves in a few days, and asymptomatic neonates with serum calcium levels > 7 mg/dL or ionized calcium > 3.5 mg/dL rarely require treatment. Those term infants with levels < 7 mg/dL and preterm infants with calcium < 6 mg/dL (< 1.5 mmol/L) should be treated with 2 mL/kg of 10% calcium gluconate (200 mg/kg) by slow IV infusion over 30 min. Too-rapid infusion can cause bradycardia, so heart rate should be monitored during the infusion. The IV site should also be watched closely because tissue infiltration by a calcium solution is irritating and may cause local tissue damage or necrosis. Manifestations of calcium infiltration include skin redness, calcification, and necrosis or slough; there can be radial nerve damage at the wrist.
After acute correction of hypocalcemia, calcium gluconate may be mixed in the maintenance IV infusion and given continuously. Starting with 400 mg/kg/day of calcium gluconate, the dose may be increased gradually to 800 mg/kg/day, if needed, to prevent a recurrence. When oral feedings are begun, the formula may be supplemented with the same daily dose of calcium gluconate, if needed, by adding the 10% calcium gluconate solution into the day’s formula. Supplementation is usually required for only a few days.
Late-onset hypocalcemia treatment is addition of calcitriol or additional calcium to infant formula to provide a 4:1 molar ratio of calcium:phosphate until normal calcium levels are maintained. Oral calcium preparations have a high sucrose content, which may lead to diarrhea in preterm infants.
Neonatal hypocalcemia usually occurs within the first 2 days of life and is most often caused by prematurity, being small for gestational age, maternal diabetes or hyperparathyroidism, and perinatal asphyxia.
Neonates may have hypotonia, tachycardia, tachypnea, apnea, poor feeding, jitteriness, tetany, and/or seizures.
Diagnose by measuring total or ionized serum calcium level; measure glucose level to rule out hypoglycemia.
Treat early-onset hypocalcemia with IV 10% calcium gluconate, followed by several days of oral calcium supplementation.