Developmental Period Both of the above factors must be assessed, or be prevalent during the developmental period before a person turns 18 years old. It is estimated that about one per cent of the Victorian population has an intellectual disability. This means there are at least 40,000 Victorians with an intellectual disability. More than three quarters of these people have a mild intellectual disability. The remainder have a range of moderate, severe or profound intellectual disabilities and possibly some associated physical disabilities.
Many factors can cause intellectual disability.
However, in many cases, no identifiable cause is found. Brain injury during or after birth. Brain infection before or after birth. Disorders of metabolism, growth or nutrition. Poor diet and inadequate health care. and Drug misuse during pregnancy, includes excess alcohol and smoking.