Figure 1. Schematic illustration contrasting calcium homeostasis in human pregnancy and lactation, as compared to normal. The thickness of arrows indicates a relative increase or decrease with respect to the normal and non-pregnant state. Although not illustrated, the serum (total) calcium is decreased during pregnancy, while the ionized calcium remains normal during both pregnancy and lactation. Adapted from ref. ( 1 ), © 1997, The Endocrine Society.