FGF23 and hypophosphatemia: The resulting increase in FGF23 production does not normally result in maternal hypophosphatemia; excess FGF23 is proteolytically cleaved within osteocytes, resulting in increased secretion of C-terminal FGF23 fragments into the circulation (which is reflected in total-FGF23 concentrations), whereas concentrations of the biologically active intact hormone remain largely unaffected (27).