Final answer:
The increased need for folate during pregnancy is mainly due to the rapid growth of the fetus, which requires folate for the proper development of the neural tube, and to support the increased maternal blood volume.
Step-by-step explanation:
The pregnant woman's greater need for folate is primarily due to the rapid growth of the fetus (option c). Folate or vitamin B9 is essential for the healthy development of the neural tube in the fetus, and inadequate levels of maternal folate can result in serious neural tube defects such as spina bifida or anencephaly.
In addition to supporting the development of the neural tube, the increase in blood volume during pregnancy, which may exceed preconception volume by 30 percent, also necessitates a higher intake of folate. This is because folate plays a crucial role in the production of red blood cells, which are necessary to accommodate the increased circulatory demands of both the mother and the developing fetus.
Therefore, the Food and Nutrition Board of the Institute of Medicine recommends that all women who might become pregnant consume at least 400 µg/day of folate from supplements or fortified foods for the wellbeing of both the mother and the child.