High levels of folic acid in a mother's bloodstream can increase the chances of their child developing autism, a new study suggests. The results are startling for parents, largely because women have been told for years to take folic acid to help prevent certain birth defects.

The findings presented Wednesday at an autism research conference in Baltimore are based on a handful of families seen at only one hospital. Health experts have questioned the validity of its conclusions, and other studies have found folic acid can significantly reduce the risk of autism. 

"We are not suggesting anyone stop supplementation," said one of the researchers, M. Daniele Fallin of Johns Hopkins University's School of Public Health in Maryland.

But the findings suggest more research must be completed on the health benefits of folic acid and the link between certain vitamins and autism. The researchers tracked 1,391 children born at Boston University Medical Center from 1998 through 2013. About 100 of them were eventually diagnosed with an autism spectrum disorder. In those families, 16 mothers had very high levels of folate, and 15 had extremely high levels of vitamin B12 in their at the time of childbirth. 

"It's a finding that has plausibility," Dr. Ezra Susser, a Columbia University professor of epidemiology and psychiatry in New York, told the Associated Press.

Most of the moms in the study said they took multivitamins, but the researchers don't know why some women had such high levels of folic acid in their blood. They concluded that babies born to mothers with very high levels of the vitamin had double the risk of developing autism compared to those with normal folate levels.

Folic acid is believed to fuel cell growth and development of the nervous system. The U.S. government began recommending nearly three decades ago that women who may become pregnant take 400 micrograms of folic acid daily, after researchers concluded that certain levels of folic acid could prevent major birth defects of the baby's brain and spine. The government also requires that folic acid be added to flour, bread and other grain products. Officials claim 1,000 birth defects are prevented each year because of these policies.

Autism spectrum disorder can cause significant social and behavioral problems. There is no cure, but early intervention treatment can help. Risk factors include certain genetic or chromosomal conditions and being born to older parents, but it's unclear what causes autism. About 1 in 68 children in the United States have been diagnosed with autism.