In doing so, we examined whether two proposed risk factors - low birth weight (LBW), and in utero exposure to selective serotonin reuptake inhibitors (SSRIs) - are associated with greater behavioral homogeneity. Using data from the Western Australian Autism Biological Registry, this study found that LBW and maternal SSRI use during pregnancy were associated with greater sleep disturbances and a greater number of gastrointestinal complaints in children with ASD, respectively.