Whenever possible, it is best for pregnant women to meet the folate requirement from food.
What is the difference between folic acid and folate? Folic acid is the synthetic version of folate. As Cara Comini points out in her article on the topic, many in the medical community use the terms folate and folic acid interchangeably, but they enter the metabolic cycle in different ways, and natural folate is easier for the body to access than the synthetic version.
As we’ve previously published, we do not recommend prenatal vitamins in favor of a nutrient dense diet. The Weston A. Price Foundation teaches us more about folate in their article Vitamins for Fetal Development, which covers conception through birth.
Folate is probably the vitamin whose essential role in pregnancy is most widely known. It is necessary for the production of new DNA, and new DNA is needed for new cells. The growing life within the womb engages in constant cell division, and the mother must expand her blood supply with the production of new red blood cells as well—these activities demand a generous supply of folate. 
Adequate folate intake prevents neural tube defects, which are defects of the brain and spinal cord, and increases birth weight. It may also prevent spontaneous abortion, mental retardation and deformations of the mouth, face, and heart. 
The pregnancy RDA for folate is 600 micrograms (mcg) per day. This figure is based on the amount needed to prevent the folate concentration of the mother’s red blood cells from dropping during pregnancy and on urinary markers indicating the amount of folate being used.  It assumes that only half of the vitamin is absorbed from food, although this figure is just an average; the rate of folate absorption is dependent on zinc status.
Synthetic “folic acid” is a chemical that is not normally found in foods or the human body. It can be converted into usable forms of folate, but this conversion is limited to about 200 mcg per single dose in healthy volunteers;  it may be even more limited during long-term exposure or in certain people. Synthetic “folic acid” does not cross the placenta; folate crosses the placenta as the naturally occurring 5-methyl-tetrahydrofolate.  Since the synthetic supplements do prevent neural tube defects, pregnant women should use them if they are not going to eat folate-rich diets; whenever possible, however, it is best to meet the folate requirement from foods. Folate-rich foods include liver, legumes, and greens.
Cara Comini also points out in her article about how folic acid is making us sick: “When people have the MTHFR gene mutation, they do not turn folic acid into folate. In addition, the folic acid plugs the receptor sites in cells with an unusable form for these people. With the unusable folic acid in the receptor cites, the body is prevented from being able to use the folate that they do consume through natural food.” MTHFR is not an acronym or abbreviation for a curse word but rather a gene mutation that is relatively common escpeically among people on the autistic spectrum. “When people have this gene mutation, they do not produce the amount of the enzyme dihydrofolate reductase needed to adequately convert folic acid into the form of folate that can enter the main folate metabolic cycle.”
I turn to the Weston A. Price Foundation for guidance on what we should eat.
Meeting the Daily Folate Requirement
The folate requirement for pregnancy can be met by one of any of the following [volume after cooking]:
Chicken liver: 3.7 ounces
Calf’s liver: 2.8 – 6.4 ounces
Beef liver: 8.2 ounces
See this article which references a number of ways to prepare organ meats.
Lentils: 1.7 cups
Other legumes: 2 to 3 cups
Spinach: 2.3 cups
Asparagus: 2.3 cups
Beets: 4.4 cups. See this article about beets.
Most greens: 3 to 6 cups
Also see their chart published with more folate and choline rich meals and snacks. They point out that folate from raw milk is accompanied by a protein that doubles its absorption. Absorption of folate from food in general is dependent on zinc status.
I highly recommend the book The Nourishing Traditions of Baby and Child Care by Sally Fallon Morell and Dr. Thomas Cowan via our Amazon affiliation.
We’d love to read your questions or comments below!
 Tamura T, Picciano MF. Folate and human reproduction. Am J Clin Nutr. 2006;83(5):993-1016.
 Standing Committee on the Scientific Evaluation of Dietary Reference Intakes and its Panel on Folate, Other B Vitamins, and Choline and Subcommittee on Upper Reference Levels of Nutrients, Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press (1998) pp. 196-305.
 Kelly P, McPartlin J, Goggins M, Weir DG, Scott JM. Am J Clin Nutr. 1997;65(6):1790-5.