Autistic people may be severely impaired in some respects but average, or even superior, in others.Clinicians consider assessment for ASD when a patient shows:

regular difficulties in social interaction or communication
restricted or repetitive behaviors (often called "stimming")
resistance to changes or restricted interestsThese features are typically assessed with the following, when appropriate:

problems in obtaining or sustaining employment or education
difficulties in initiating or sustaining social relationships
connections with mental health or learning disability services
a history of neurodevelopmental conditions (including learning disabilities and ADHD) or mental health conditions.There are many signs associated with ASD; the presentation varies widely:
Atypical eating is also common, but it does not need to be present to make a diagnosis.In addition, a small percentage of autistic people can exhibit notable ability, for example in mathematics, music or artistic reproduction, which in exceptional cases is referred to as savant syndrome. Developmental course
There are two possible developmental courses of ASD. One course of development is more gradual in nature, with symptoms appearing fairly early in life and persisting. A second course of development is characterized by normal or near-normal development before onset of regression or loss of skills, which is known as regressive autism. Gradual autism development
Most parents report that the onset of autism features appear within the first year of life. This course of development is fairly gradual, in that parents typically report concerns in development over the first two years of life and diagnosis can be made around 3–4 years of age.
These risk factors include maternal gestational diabetes, maternal and paternal age over 30, bleeding during pregnancy after the first trimester, use of certain prescription medication (e.g. valproate) during pregnancy, and meconium in the amniotic fluid. While research is not conclusive on the relation of these factors to autism, each of these factors has been identified more frequently in children with autism, compared to their siblings who do not have autism, and other typically developing youth. While it is unclear if any single factors during the prenatal phase affect the risk of autism, complications during pregnancy may be a risk.Low vitamin D levels in early development have been hypothesized as a risk factor for autism.There are also studies being done to test if certain types of regressive autism have an autoimmune basis.Maternal nutrition and inflammation during preconception and pregnancy influences fetal neurodevelopment. Intrauterine growth restriction is associated with ASD, in both term and preterm infants. Maternal inflammatory and autoimmune diseases may damage fetal tissues, aggravating a genetic problem or damaging the nervous system.Exposure to air pollution during pregnancy, especially heavy metals and particulates, may increase the risk of autism. Environmental factors that have been claimed without evidence to contribute to or exacerbate autism include certain foods, infectious diseases, solvents, PCBs, phthalates and phenols used in plastic products, pesticides, brominated flame retardants, alcohol, smoking, illicit drugs, vaccines, and prenatal stress. Some, such as the MMR vaccine, have been completely disproven.