The primary reason for women of childbearing age to take folic acid is to greatly reduce the risk of children developing neural tube defects (NTDs) in the early stages of pregnancy. The full effects of the B vitamin are felt when taken at least one month before conception through the first trimester.

A 2019 study suggests that taking folic acid through the second and third trimester of the pregnancy can also help with the child’s cognitive function as they age.

According to researchers from Ulster University in Northern Ireland, University College Dublin, and Trinity University in the Republic of Ireland, children of mothers who took folic acid throughout the entire pregnancy scored significantly higher on cognitive tests at ages 3 and 7, compared to mothers who took a placebo.

Researchers studied the results of 119 mother-child pairing, including 70 children at age seven, and 39 children at age three.

The children at age seven whose mothers had taken the daily recommended amount of folic acid (400 mcg) had significantly higher scores in word reasoning compared to the children whose mothers took the placebo.

The children at age three also tested higher for cognition than those of mothers who took the placebo.

Both age groups also had higher than average scores on both the Bayley’s Scale of Infant and Toddler Development (BSITD-III) and the Wechsler Preschool and Primary Scale of Intelligence (WPPSI-III).

Source: BMC Medicine. Volume 17, Article 196.

“Effect of continued folic acid supplementation beyond the first trimester of pregnancy on cognitive performance in the child: a follow-up study from a randomized controlled trial (FASSTT Offspring Trial)”

What this means for moms-to-be

This was a small follow-up study, so more research is needed before experts change their advice. For now, the U.S. Preventive Services Task Force recommends daily folic acid starting at least one month before conception and continuing through the first two to three months of pregnancy, the window when neural tube defects can occur. Many people keep taking a prenatal vitamin with folic acid throughout pregnancy, and ACOG notes that eating healthy foods and taking a prenatal vitamin every day should supply the vitamins and minerals you need during pregnancy.

During pregnancy, your total folate need rises to 600 mcg DFE a day from all sources, according to the NIH Office of Dietary Supplements. Talk with your provider about which prenatal vitamin is right for you and how long to take it.

Updated October 2026. This article is for general information and is not a substitute for advice from your health care provider.

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