Michael Davies of the University of Adelaide's Robinson Institute said public health guidelines recommend women consume a supplemental dose of 400 micrograms of folic acid per day in the month preceding and during the first trimester of pregnancy to reduce the risk of neural tube defects in children.
The study involved more than 500 women whose maternal diet and supplements were assessed twice during their pregnancy, with follow-up on their child's asthma status at 3.5 years and 5.5 years.
Asthma was reported in 11.6 percent of children at 3.5 years and 11.8 percent of children at 5.5 years. Nearly one-third of these children reported persistent asthma.
"Our study supports these guidelines, as we found no increased risk of asthma if folic acid supplements were taken in pre- or early pregnancy," Davies said in a statement.
"However, these guidelines may need to be expanded to include recommendations about avoiding use of high-dose supplemental folic acid in late pregnancy."
The findings are published in the American Journal of Epidemiology.