"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.
Women wishing to conceive
are already recommended to start taking folic acid supplements as soon as possible - at least four weeks before they begin trying for a baby.
Good stores of folic acid has been proven to significantly reduce the risk of spina bifida and other major birth
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.