Early detection of ASD leads to earlier intervention which in turn may lessen, or even eliminate, ASD symptoms for some children. Yet identifying the earliest signs of ASD has been challenging. Some ASD patients develop symptoms before their first birthday; in others, symptoms become apparent later in the second or even third year of life. Children with ASD can be reliably diagnosed by 2 years of age, but research suggests that some screening tests can be helpful at 18 months or even younger.
Source: Annie Shic