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(CNN) —  

Taking prenatal vitamins during the first month of pregnancy is associated with a lower risk of developing autism in children who are at high risk for the disorder, according to a new study.

Researchers followed 241 children whose older siblings had a diagnosis of autism and who therefore had an increased risk of being diagnosed with the disorder. The researchers evaluated the children’s development starting at 6 months through 3 years of age. At the same time, the moms were asked through phone interviews and mailed questionnaires about prenatal vitamin use.

Approximately 1 in every 4 children enrolled in the study went on to be diagnosed with autism spectrum disorder, similar to the rate of 1 in 5 for younger siblings of children with autism reported in prior studies. Of the children whose mothers took prenatal vitamins in the first month of the pregnancy, 14.1% went on to develop autism, compared with 32.7% in children whose mothers did not.

Autism spectrum disorder is a developmental disability that results in behavioral and social changes, including communication. According to the US Centers for Disease Control and Prevention, an estimated 1 in 59 children in the US has autism. The condition affects many more boys than girls.

In the new study, the reduction in the risk of developing autism also seemed to be greater for the children whose moms took greater doses of folic acid and iron during pregnancy, suggesting that there might be at least a partial dose effect. This means prenatal vitamins with greater concentrations of folic acid and iron seemed to work better at preventing autism in children at risk.

Taking prenatal vitamins early was also associated with less severe symptoms and higher cognitive scores in children who were ultimately diagnosed with autism.

“This is a very important study,” said Dr. Pankhuree Vandana, child psychiatrist and medical director of the Autism Center at Nationwide Children’s Hospital, who wasn’t involved in the research. The results add to a body of literature suggesting that folic acid – a supplement found in most prenatal vitamins – can be protective against developmental disorders like autism, she added.

Compared with mothers who did not take prenatal vitamins early, the mothers in the study who did were more likely to have obtained a bachelor’s degree or higher, own a home, have private health insurance and have had an intentional pregnancy.

Children whose siblings have autism spectrum disorder are also at increased risk of conditions such as developmental delay, attention deficit and intellectual disability. Taking prenatal vitamins did not seem to decrease this risk in the study, which was published Wednesday in the medical journal JAMA Psychiatry.

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Vandana worries that the study is relatively small and cautions that the results may not hold true in the general population. In addition, she points out that over the past few years, expectant moms have continued to take prenatal vitamins at similar or higher rates, and yet the incidence of autism has continued to increase. However, Vandana says, this is a reminder that prenatal vitamins and the nutrients they provide are one of many factors that can potentially influence the development of autism.

Given the safety, low cost and benefits of prenatal vitamins, Vandana does encourage expectant moms to take them as early as possible.

“It is an easy thing to do … and it might actually help, even when the odds are stacked up against you.”