Antenatal factors. Some syndromes cause autistic spectrum disorder & intellectual disability. Chromosomal microarrays find genetic errors in ~15% of kids with ASD. Maternal low folate (folic acid) levels at conception, rubella, "flu", obesity, advanced age & alcohol/drug use from 3 wks. Post-conception-term are some epigenetic factors that alter function, but not structure or sequence, of fetal genes & increase risk of ASD.