Disorders of calcium homeostasis in the fetus and neonate.

The physiological mechanisms involved in the alterations in calcium homeostasis during pregnancy are complex. The fetal acquisition of calcium, for skeletal growth, is obtained by an increase in intestinal calcium absorption in the mother with transplacental calcium transfer to the fetus. The regulation of calcium homeostasis during the transition from the intrauterine to the extrauterine environment is complex and poorly understood. Within the first few hours of life the serum calcium concentrations begins to fall progressively reaching a "trough" value by the second or third day of life and then increases to normal values by the tenth day of life. In some neonates the fall in calcium concentration is sufficient to be associated with either tetany or convulsions. Hypocalcemia is probably the commonest disturbance of calcium homeostasis that occurs in the neonate and can be subdivided into three main groups on the basis of the etiological mechanism involved. Other disorders of calcium homeostasis that may affect the neonate include hypoparathyroidism, either congenital or acquired, pseudohypoparathyroidism, and vitamin D deficiency. Hypercalcemia may occur, but is a relatively rare occurrence in the neonate.