Chapter 18: Pregnancy and Lactation Christopher S. Kovacs and Henry M. Kronenberg

Figure 1 Figure 1 Schematic illustration contrasting calcium homeostasis in human pregnancy and lactation compared with normal. The thickness of arrows indicates a relative increase or decrease with respect to the normal and nonpregnant state. Although not shown, the serum (total) calcium is decreased during pregnancy, whereas the ionized calcium remains normal during both pregnancy and lactation. (Adapted with permission from The Endocrine Society © 1997: Kovacs CS, Kronenberg HM 1997 Maternal-fetal calcium and bone metabolism during pregnancy, puerperium and lactation. Endocr Rev 18:832–872.) From the Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, 7 th Edition.

Figure 2 Figure 2 The breast is a central regulator of skeletal demineralization during lactation. Suckling and prolactin both inhibit the hypothalamic gonadotropin-releasing hormone (GnRH) pulse center, which in turn suppresses the gonadotropins (luteinizing hormone [LH] and follicle-stimulating hormone [FSH]), leading to low levels of the ovarian sex steroids (estradiol and progesterone). PTHrP production and release from the breast is controlled by several factors, including suckling, prolactin, and the calcium receptor. PTHrP enters the bloodstream and combines with systemically low estradiol levels to markedly upregulate bone resorption. Increased bone resorption releases calcium and phosphate into the blood stream, which reaches the breast ducts and is actively pumped into the breast milk. PTHrP also passes into milk at high concentrations, but whether swallowed PTHrP plays a role in regulating calcium physiology of the neonate is unknown. Calcitonin (CT) may inhibit skeletal responsiveness to PTHrP and low estradiol. (Reprinted with permission from Springer Science and Business Media ©2005: Kovacs CS 2005 Calcium and bone metabolism during pregnancy and lactation. J Mammary Gland Biol Neoplasia 10:105–118.) From the Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism, 7 th Edition.