Final answer:
The fetal demand for iron reaches its peak during the third trimester due to rapid growth and the need to prepare for oxygen transport once the baby is born.
Step-by-step explanation:
Fetal demand for iron is highest during the third trimester of pregnancy. This period is characterized by rapid fetal growth requiring increased nutrients to support the developing fetal structures and preparing the fetus for life outside the womb. Iron is a critical nutrient as it is essential for the production of hemoglobin the protein in red blood cells that carries oxygen.
Since fetal hemoglobin can bind with oxygen at lower pressures, it is particularly important for the fetus to have an adequate supply for oxygen transport from the mother's blood in the placenta. Stores of nutrients are established early during pregnancy in order to accommodate the increased fetal demand later on. In the third trimester, there's a significant increase in the rate of red blood cell production to prepare the newborn for independent circulation following birth, hence the heightened requirement for iron.