Dwarfism occurs when an organism is extremely small. In humans, it is sometimes defined as an adult height of less than 147 centimetres (4 ft 10 in), regardless of sex; the average adult height among people with dwarfism is 122 centimetres (4 ft 0 in), although some individuals with dwarfism are slightly taller. Disproportionate dwarfism is characterized by either short limbs or a short torso. In cases of proportionate dwarfism, both the limbs and torso are unusually small. Intelligence is usually normal, and most have a nearly normal life expectancy. People with dwarfism can usually bear children, although there are additional risks to mother and child, dependent upon the underlying condition.