Developmental programming explains WHY the nutritional environment in pregnancy leaves decades-long marks on the child; how much of each nutrient and when is a separate dosing table.
The four gates are about whether a nutrient gets delivered at all; the per-nutrient dosing table is a separate matter, and only the two together are actionable.
Blood volume expands by about 50%, and the fetus and placenta build their own blood on top of that — pushing the iron recommendation from 18 mg/day to 27. That isn't 'a bit more', it's a different balance sheet.