LOS ANGELES — Mothers who took folic acid supplements around the time they became pregnant were less likely to have children with an autism spectrum disorder, a new study has found.

Researchers in Norway examined health records of more than 85,000 children born there between 1999 and 2009 to see whether they had some kind of autism diagnosis. They also looked at questionnaires completed by their mothers to see how much folic acid they were consuming in the month before they became pregnant and during the first eight weeks of pregnancy, a critical period of embryonic brain development. Health officials in Norway recommend that pregnant women (and women who are trying to get pregnant) take 400 micrograms of folic acid per day.

Among the 85,176 children in the study, 270 (or 0.32 percent) received an ASD diagnosis — 114 (0.13 percent) had autistic disorder, 56 (0.07 percent) had Asperger syndrome and 100 (0.12 percent) were diagnosed with “pervasive developmental disorder-not otherwise specified,” or PDD-NOS.