Final answer:
During pregnancy, the requirement for iron often cannot be met through diet alone and may need supplementation, in contrast to calcium which can generally be met through dietary sources.
Step-by-step explanation:
During pregnancy, a woman's need for many nutrients increases, which includes macronutrients such as sodium and potassium for nerve and muscle function, and iron for hemoglobin in red blood cells. However, iron is often the mineral that is unlikely to be met through diet alone during pregnancy. Pregnant women typically need more iron due to the increased blood volume and need to supply oxygen to the fetus, which makes it a critical nutrient during this time. Calcium requirement also increases, but it is usually easier to meet through diet compared to iron.