The authors conducted a questionnaire using two independent samples of children from south China and north China. The parents received a questionnaire, which asked questions regarding the general conditions of the children, parents' maternal pregnant and prenatal conditions, the child's development, history of diseases, medications, history of pregnancy and prenatal exposure to adverse events, history of abortions and diseases, and so on. The study found two new risk factors: maternal chemical exposure and induced abortion are associated with increased risk of autism. The authors conclude that these factors are common and preventable through various means, such as reducing environmental exposure, improving reproductive health, or increasing access to contraceptives.