Published online by Cambridge University Press: 10 December 2009
Disorders of mineral homeostasis
Fetal mineral homeostasis is closely linked to that of the mother. In the pregnant woman and the fetus there is an intimate and delicate relationship amongst the calciotropic hormones, growth factors, and the minerals Ca, P, and Mg. Any perturbation of maternal or placental homeostatic mineral balance may affect that of the fetus and may have metabolic sequelae in the fetus manifesting in the neonatal period and infancy.
Disorders of calcium homeostasis
A wide variety of factors can cause significant disturbances in calcium and bone homeostasis in the fetus and neonate.
Maternal hypocalcemia
Maternal hypocalcemia results in fetal hypocalcemia, which stimulates the fetal parathyroid glands to synthesize and secrete more parathyroid hormone (PTH to achieve normocalcemia. PTH does not appear to cross the placenta in either direction. Causes of maternal hypocalcemia are listed in Table 16.1. Impaired secretion of PTH because of hypoparathyroidism or magnesium depletion and resistance to PTH because of mutant receptors, as in pseudohypoparathyroidism, result in maternal hypocalcemia. Hypocalcemia may also be a manifesting feature of abnormal vitamin D deficiency; in particular, maternal vitamin D deficiency may be caused by insufficient sunlight exposure, inadequate dietary intake, or malabsorption. Maternal liver disease may be associated with defective 25-hydroxylase activity resulting in low serum 25-hydroxyvitamin D (25-OHD) concentration, hypocalcemia, and rickets.
Defective 1 alpha-hydroxylase activity may be caused by renal or parathyroid gland diseases.
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