Hypocalcemia in Newborns
Definition
Hypocalcemia is a disorder where there is a lowered blood calcium levels in newborns. It is defined as a total serum calcium concentration of less than 7 mg/dl. It is divided into early onset which occurs in the first 72 hours of life and late onset at about 5 to 10 days of age.
Incidence
Occurrence of this disorder is about 30% in infants with very low birth weight (<1500 g) and approximately 89% in premature infants. A very high prevalence rate is also noted in infants born with a diabetic mother.
Review of Anatomy and Physiology
Parathyroid glands are masses of glandular tissues found on the posterior surface of the thyroid gland. The parathyroids secrete parathyroid hormone (PTH) or parathormone which regulates the calcium levels in the blood. PTH is called a hypercalcemic hormone as it acts to increase the serum calcium blood levels.
Normal calcium levels in the blood vary with age: (from Saunder’s Foundations of Maternal-Newborn Nursing by Murray and McKinney, 4th Ed)
Cord = 9-11.5 mg/dl
Newborn, 3-24 hours = 9-10.6 mg/dl
Newborn, 24-28 hours = 7-12 mg/dl
Newborn, 4-7 days = 9-10.9 mg/dl
When the calcium levels in the blood drop, the parathyroids release PTH, which stimulates osteoclasts (bone cell destruction) to break down bone matrix and release calcium in the blood. The PTH also stimulates the kidneys and intestine to absorb more calcium. In contrary, the hormone that functions to decrease calcium in the blood (hypocalcemic hormone) is the calcitonin. Calcitonin is produced by the thyroid glands which cause calcium to be deposited in the bones.
Pathophysiology
Causes
Early Onset Hypocalcemia
- Maternal diabetes (gestational or insulin dependent) related to increased calcium demands of a macrosomic infant. Hypocalcemia tends to accompany the hypoglycemia that occurs in infants of a diabetic mother.
- Perinatal Asphyxia or stress
Perinatal asphyxia (suffocation) or stress could lead to anoxia. Phosphorous is released with anoxia, thus elevating its level. As phosphorous levels rise, calcium levels drop. This may also be related to renal insufficiency, metabolic acidosis and diminished parathyroid hormone secretion.
- Prematurity
Preterm babies are at an increased risk of early onset hypocalcemia in the extrauterine life. This may be related to immature parathyroid glands, premature separation of trans-placental supply, diminished responsiveness of target organs to parathyroid hormone, increased calcitonin, poor intake and decreased responsiveness to Vitamin D.
- Intrauterine growth retardation
Late Onset Hypocalcemia
- Vitamin D deficiency
This is possible related to malabsorption, renal insufficiency, maternal Vitamin D deficiency or hepatobiliary disease. Vitamin D is needed for the absorption of calcium, without it the body cannot utilize calcium.
- High phosphate formula
Phosphorous and calcium levels are maintained in an inverse proportion to each other in the bloodstream. If phosphorous levels rise, calcium levels decrease. If calcium levels elevate, phosphorous levels drop.
If an infant is fed with a phosphate-rich formula or cow’s milk tendencies of having a low calcium level in the blood may result. Whole cow’s milk has 7 times more phosphate load than breastmilk.
- Low magnesium levels or hypomagnesemia
- Congenital hypoparathyroidism
- Real disease or insufficiency
