Figure 2. Schematic depiction of longitudinal changes in calcium, phosphorus, and calciotropic hormone levels during human pregnancy. Shaded regions depict the approximate normal ranges. PTH does not decline in women with low calcium or high phytate intakes, and may even rise above normal. Calcidiol (25OHD) values are not depicted; most longitudinal studies indicate that the levels are unchanged by pregnancy, but may vary due to seasonal variation in sunlight exposure and changes in vitamin D intake. FGF23 values cannot be plotted due to lack of data. Reproduced with permission from (1).