It is suggested that women who have the potential of getting pregnant take a supplement of 400-800 mcg of folic acid a day to prevent birth defects of the brain and spinal cord, called neural tube defects (NTDs). Studies also suggest that folic acid may help prevent some other birth defects as well, it may also prevent autism spectrum disorder, and prevent cleft lip and palate. Folic acid intake is important during pregnancy.

• To be effective, folic acid must be taken several months before pregnancy so that adequate levels are achieved when ovulation happens.
• Folic acid is recommended for all women of childbearing age because 50% of pregnancies are unplanned. Folic acid is not known to have an impact on fertility.
• Those who previously had a child with a neural tube defect should take 4 mg folic acid (10-times the recommended amount of 400 mcg) per day.
• Folic acid mostly works if it's taken before pregnancy and in the first few weeks of pregnancy. It is to late to prevent NTDs if you start taking it after the pregnancy test is positive.
• Since most malformations originate in the first month of pregnancy, before many women know they are pregnant, it is important for a woman to have enough folic acid in her system before conception.
• Some studies have also shown that folic acid  when taken more than 3 months before conception, significantly reduces many pregnancy complications such as miscarriage, birth defects, preterm births, stillbirths, and neonatal mortality.

• And there is a study showing that folic acid supplementation can improve your fertility if you start taking it up to one year before pregnancy begins. 
• Folic acid is the synthetic form of folate which is a B vitamin found naturally in a variety of foods, including leafy green vegetables such as, collards, kale, turnip greens, romaine lettuce, broccoli, and asparagus. It is also found in liver, beans, citrus fruits and juices, whole grain products and wheat germ. Folic acid is important for the formation of red and white blood cells.
• The average folate contained in a regular well-balanced diet is about 200 mcg, but a large amount of it is not absorbed by your body, and the amount of folate in your diet is not sufficient to fill your needs before and during pregnancy (1/2 cup of vegetables and beans, for example, contains only 30-150 micrograms of folate). Therefore, women who have the potential to get pregnant need to supplement their diet with additional folic acid if they want to decrease their risk of having a baby with neural tube defects and other malformations.
• Because the neural tube develops very early in the embryo's life, usually within 2-4 weeks after conception, malformations can occur in an embryo before you miss your period, even before you realize that you are pregnant. Women have been told for many years now to take folic acid before pregnancy, but many do not seem to understand that doing so can prevent fetal malformations. Therefore, many women have come to believe that taking folic acid before pregnancy will improve fertility when in actuality it is suggested in order to decrease certain malformations in your baby.
• There is no conclusive evidence that taking folic acid has an impact on fertility

How much folic acid supplement should I take?

Research has shown taking a daily folic acid supplement not only decreases the risk of having a baby with a neural tube defect (NTD), it also decreases the risk of heart defects, cleft lip/palate, and an autism spectrum disorder. Carefully read the ingredients of the vitamin supplements you take. It is recommended to take between 400-800 mcg folic acid supplement each day. Most prenatal vitamin supplements have at least 400 micrograms of folic acid, and many have more than that. 

• If you previously had an affected child with an autism spectrum disorder, heart defect, and/or neural tube defect then it's recommended to take about 4-5,000 micrograms (4-5 mg) folic acid a day 3 months prior to conception.
• You shouldn’t exceed 5,000 micrograms (5 mg) of folic acid a day, as it may mask certain blood problems. Read the labels of cereals that you eat. The nutrition information on food and dietary supplement labels can help you determine whether you are getting enough folic acid. Taking an adequate amount of folic acid daily will help you decrease the risk of many cases of fetal malformations.

Since there are many factors that can affect a pregnancy (including genetics, the environment, an overall good diet, and responsible behavior), you need to realize that folic acid alone cannot always ensure a healthy baby.

Folic Acid Pregnancy Studies

• Folic Acid is Important for Trying to Conceive (TTC) and Pregnant Women 
• Delay in Language Development Reduced with Folic Acid
• Folic Acid Reduces Risk of Autism Disorder
• Dietary Folic Acid Intake Across Three Generations
• Folic Acid Linked to Autism Prevention
• Folic Acid Absorption Affected by Medications
• Association Between Oxidized LDL and Folate During Pregnancy
• Dietary Folate Impact on Reproductive Function
• Beyond Preventing Birth Defects: Folate May do More for Child's Health

Further Reading

• Folic Acid Information
• Can I Take Too Much Folic Acid During Pregnancy?
• Best Time to Take Folic Acid During Pregnancy
• Folate (Serum) Levels During Pregnancy
• Folate - Red Cell (Whole Blood) Levels During Pregnancy 
• The B Vitamin No Woman Should be Without