"Maternal use of supplements containing folic acid within the period from four weeks before, to eight weeks after conception was associated with a substantially reduced risk of severe language delay in children at age 3 years," said the study's lead author Christine Roth.
Good stores of folic acid has been proven to significantly reduce the risk of spina bifida and other major birth defects.
This latest study was conducted over a nine year period and followed nearly 39,000 children up to the age of three.
Mothers were asked to assess their children's language skills using a six-point language scale. Children classified as having a severe language delay were those who, by the age of three, were only using one word or unintelligible sounds.
The study found 204 cases of severe language delay.
Only 0.4% of women who took folic acid supplements saw severe language delay in their children.
The results of Ms Roth's study have been published by the Journal of the American Medical Association.