Calcium and Phosphate Metabolism and Related Disorders During Pregnancy and Lactation

Pregnancy and lactation require women to provide calcium to the fetus and neonate in amounts that may exceed their normal daily intake. Specific adaptations are invoked within each time period to meet the fetal, neonatal, and maternal calcium requirements. During pregnancy, intestinal calcium and phosphate absorption more than double, and this appears to be the main adaptation to meet the fetal demand for mineral. During lactation, intestinal calcium absorption is normal. Instead, the maternal skeleton is resorbed through the processes of osteoclast-mediated bone resorption and osteocytic osteolysis, in order to provide most of the calcium content of breast milk. In women this lactational loss of bone mass and strength is not suppressed by higher dietary intakes of calcium. After weaning, the skeleton appears to be restored to its prior bone density and strength, together with concomitant increases in bone volumes and cross-sectional diameters that may offset any effect of failure to completely restore the trabecular microarchitecture. These maternal adaptations during pregnancy and lactation also influence the presentation, diagnosis, and management of disorders of calcium, phosphorus, and bone metabolism such as primary hyperparathyroidism, hypoparathyroidism, vitamin D deficiency, and phosphate disorders. Pregnancy and lactation can also cause pseudohyperparathyroidism, a form of hypercalcemia that is mediated by parathyroid hormone-related protein, produced in the breasts or placenta during pregnancy, and by the breasts alone during lactation. Although rarely women may experience fragility fractures during pregnancy or lactation, for most women parity and lactation do not affect the long-term risks of low bone density, osteoporosis, or fracture. For complete coverage of all related areas of Endocrinology, please visit our on-line FREE web-text, WWW.ENDOTEXT.ORG.