In 2013, data from a massive study of more than 85,000 children in Norway suggested that women who take folic acid supplements early in pregnancy lower their risk of having children with autism. In September, an analysis of a similarly designed study of more than 35,000 mothers and babies in Denmark found no link between prenatal vitamins and autism risk, raising doubts about the Norwegian finding. Science is always an iterative process, but in the case of pinpointing risk factors for autism, progress has been remarkably slow and difficult.