CHAPTER 28: Pregnancy and Calcium

During normal human pregnancy, the fetus accumulates 30 g of calcium. To meet this fetal demand, major maternal adaptations in calcium metabolism take place. Most significant among these is doubling of intestinal calcium absorption during pregnancy associated with increased levels of 1,25-dihydroxyvitamin D₃. In addition, there may be increased resorption of trabecular bone during pregnancy. This, however, is not associated with adverse long-term outcomes such as osteoporosis and fractures. Calcium is actively transported across the placenta by a complex and elaborate system of proteins, allowing the fetus to maintain calcium levels higher than the mother. The regulation of placental calcium transport is largely unknown. In mothers with sufficient intake of dietary calcium, these adaptations are considered adequate for the calcium needs of the mother and fetus and the need for supplemental calcium in these mothers is controversial. In mothers with a decreased intake of dietary calcium, calcium supplementation has been demonstrated to reduce the incidence of gestational hypertensive disease and preterm birth. Disorders of calcium metabolism during pregnancy such as hyper- and hypoparathroidism, may present diagnostic and management challenges due to the maternal adaptations in calcium metabolism. This chapter will review the calcium metabolism and adaptations that occur during pregnancy, followed by a discussion of pathological calcium states during pregnancy.