Etiological implication of maternal age and birth order in infantile autism.

Birth orders and maternal ages of the 113 autistic patients were compared with those of the general population. An excess of mothers aged 35 or older was observed in the autistic group, though the mean maternal age for the whole group was very similar to those of the general population. A deviation from average in birth order was observed in autistics. Significantly more autistics were products of at-risk pregnancies (defined as either first, fourth, or later born, or born to mothers aged 30 or older) than the base population. The results suggest that at least some environmental factors are involved in the causation of autism. The findings support the idea that a multifactorial mechanism is responsible for some or all of the cases.